Hadith according to them is categorized into Mutawatir and Ahad.
The definition of Mutawatir according to them:
عبارة عن مجيئ الواحد بعد الواحد بفترة بينهما وفصل، ومنه قوله عز من قائل: ثُمَّ أَرْسَلْنَا رُسُلَنَا تَتْرَىٰ أي رسولا بعد رسول بزمان بينهما
To come one after the other with a time between the two and a separation, like in the verse of Allah subhanahu wa ta ‘ala the almighty, “Thereafter, we sent our prophets in succession,” i.e. prophet after prophet with a time-gap between them.
خبر جماعة بلغوا في الكثرة إلى حد أحالت العادة اتفاقهم وتواطؤهم على الكذب، ويحصل بإخبارهم العلم، وإن كان للخبر مدخلية في إفادة تلك الكثرة العلم
هذا وقد اتفق أكثر العقلاء على إمكان تحقق الخبر المتواتر وحصول العلم به، والقائلون بإمكان تحقق الخبر المتواتر، وحصول العلم به، اختلفوا فقال أكثرهم: إنه العلم الضروري، وقال جمع: إن ذلك العلم النظري
The report of a group so abundant that convention deems it impossible for so many people to agree and concur upon lying. Hence, categoricity is obtained by their reporting, even though the report itself also plays a role in that exceeding number giving the benefit of categoricity.
Having said that, most intelligent people agree on the possibility of a report being Mutawatir and categoricity being obtained through it. However, there is difference of opinion amongst those who aver that such a Mutawatir narration can occur about the nature of the categoricity which is obtained through it. Hence, most of them say: It is self-evident categoricity, whereas a group says that it is discursive categoricity.
They have mentioned several requisites for a Mutawatir narration to be of epistemological certainty, some related to the listener and some to the transmitters.
They are two:
From the aforementioned, the influence of the false belief of the Rawafid on the Mutawatir narration is evident. For one of the requirements according to them is that the Mutawatir narration not be preceded by a doubt, or by the blind following of the receiver which compels him to negate the purport of the narration or the narration itself. We can gauge this influence when they say that it is a strong requisite by way of which the argument of our opponents to prove the absence of the emphatic appointment of Amir al Mu’minin ‘alayh al Salam is debunked. Hence, in the case of the mass-transmitted fact that Nabi salla Llahu ‘alayhi wa sallam did not emphatically appoint anyone as the Imam after him, the blame is directed to the receivers, whereby they achieve their objective of deeming this fact untannable. Whereas on the other hand, we find them averring that the hadith of Thaqalayn and Ghadir are Mutawatir.
In essence, the belief of Imamah engenders them to discard that which is actually Mutawatir and accept that which in itself is not Mutawatir as Mutawatir, as long as it is related to this belief.
Ibn Taymiyyah mentions:
والقوم من أكذب الناس في النقليات ومن أجهل الناس في العقليات يصدقون من المنقول بما يعلم العلماء بالاضطرار أنه من الأباطيل ويكذبون بالمعلوم من الأضطرار المتواتر أعظم تواتر في الأمة جيلا بعد جيل ولا يميزون في نقلة العلم ورواة الأحاديث والأخبار بين المعروف بالكذب أو الغلط أو الجهل بما ينقل وبين العدل الحافظ الضابط المعروف بالعلم بالآثار
These people are the biggest liars in text-based matters and the most ignorant in logic-based matters. They believe in such transmitted reports which the scholars intuitively know to be false, and they belie such known facts which the scholars intuitively know to be established, due to it being transmitted by way of mass-transmission in the Ummah from one generation to another. Likewise, in the transmitters of knowledge and the narrators of narrations and reports they cannot distinguish between a narrator who is infamous for lying, excessively erring, or is ignorant of what he narrates, and a person who is an upright retainer who is precise in his transmission and is known to have a good knowledge-base about narrations.
They have defined this category as:
هو ما لا ينتهي إلى حد التواتر سواء كان الراوي له واحد أو أكثر
A narration which does not reach the extent of Tawatur (mass-transmission), irrespective of whether its narrator is one or many.
The narrations of this category according to the Rawafid are graded with four gradings. These four gradings are the primary types to which every other categorization returns. These gradings are: Sahih, Hassan, al Muwaththaq, Da’if.
They have defined it as follows:
هو ما اتصل سنده إلى المعصوم بنقل العدل الإمامي عن مثله في جميع الطبقات حيث تكون متعددة
A narration whose transmission consistently reaches the infallible through the transmission of an upright Imami from his like in all the links when they happen to be many.
And some have added other requirements, which are as follows:
However, you are well aware that the requirement of the uprightness of the narrator suffices on this behalf, for a negligent person who deserves to be discarded is never approbated by the scholars of transmitter biographies. Also, uprightness demands the truthfulness of the narrator, and him not being negligent and careless in assimilation and transmission. Yes, if the requirement of being a precise retainer is added for clarification, the definition would be stronger.
إن عدم الشذوذ شرط في اعتبار الخبر، لا في تسميته صحيحا
The absence of anomaly is a requirement for considering the narration itself, not for dubbing it Sahih.
Hence, with the clause of ‘consistency of transmission’ an inconsistent chain is precluded wherever that inconsistency may occur, and thus such a narration will not be dubbed Sahih even though its narrators are of the level of Sahih.
The clause ‘infallible’ includes the Nabi salla Llahu ‘alayhi wa sallam and the Imam.
And with the clause ‘the transmission of an upright person’ Hassan narrations are excluded.
And with the clause ‘Imami’ Muwaththaq is excluded.
And with the clause ‘in all the links’ a narration in one of whose links a narrator of a lower ranking is found is precluded, for because of that it will be graded with a grading best suited for it, but it will not be considered Sahih. (Till the end)
So, in conclusion: they concur upon the following requirements:
The influence of the doctrine of Imamah here is clear, i.e. in the requisite of the narrator being Imami alongside the specification of the infallible (included in which are the Imams). So, no narration can progress to the level of Sahih until all the narrators are Rawafid in all the links.
To further explain, the first scholar to coin the categories of hadith according to them was Ibn al Mutahhar al Hilli (d. 726 A.H). He clarifies the reason for this requirement saying:
لا تقبل رواية الكافر، وإن علم من دينه التحرز عن الكذب، لوجوب التثبت عند الفاسق، والمخالف من المسلمين، إن كفرناه فكذلك، وإن علم منه تحريم الكذب – خلافاً لأبي الحسن لاندراجه تحت الآية، وعدم علمه لا يخرجه عن الاسم، ولأن قبول الرواية تنفيذ الحكم على المسلمين، فلا يقبل كالكافر الذي ليس من أهل القبلة. احتج أبو الحسن بأن أصحاب الحديث قبلوا أخبار السلف كالحسن البصري وقتادة وعمر بن عبيد، مع علمهم بمذهبهم، وإنكارهم على من يقول بقولهم، والجواب المنع من المقدمتين، ومع التسليم فنمنع الإجماع عليه وغيره ليس بحجة. والمخالف غير الكافر لا تقبل روايته أيضاً لاندراجه تحت اسم الفاسق
The narration of a Kafir will not be accepted, even though he is known in his religion to avoid lying, due to investigation being compulsory of a Fasiq, an imposter. And the opponent from the Muslims, if we excommunicate him, then likewise (his narration will not be accepted), even though abstaining from lying is known about him (contrary to the view of Abu al Hassan) due to him also being included in the purview of the verse; since not knowing a person (to be a liar) does not preclude him from the disparaging label (of Fisq). And because the acceptance of a narration entails executing a ruling upon the Muslims, hence his narration will not be accepted just as the narration of Kafir who is not from the people of the Qiblah is not accepted.
Abu al Hassan drew evidence from the fact that the scholars of hadith accepted the narrations of predecessors like al Hassan al Basri, Qatadah, and ‘Umar ibn ‘Ubaid, despite knowing their creeds and despite condemning those who held views as theirs. The answer to this is that both these premises are unacceptable. And even if we do accept them, we still do not accept that there was consensus upon this, in other than which there can be no evidence.
And an opponent who is not a Kafir, his narration will also not be accepted, due to him being included under the title of a Fasiq, imposter.
Here from we learn the following:
Not only is the effect of Imamah clear in this, but extremism and exaggeration are also quite obvious.
They have defined it as:
هو ما اتصل سنده إلى المعصوم بإمامي ممدوح مدحا مقبولا معتدا به، غير معارض بذم، من غير نص على عدالته، مع تحقق ذلك في جميع مراتب رواة طريقه، أو في بعضها بأن كان فيهم واحد إمامي ممدوح غير موثوق، مع كون الباقي في الطريق من رجال الصحيح، فيوصف الطريق بالحسن لأجل ذلك الواحد
واحترزوا بكون الباقي من رجال الصحيح عما لو كان دونه، فأنه يلتحق بالمرتبة الدنيا، كما لو كان فيه واحد ضعيف فإنه يكون ضعيفا، أو واحد غير إمامي عدل، فإنه يكون من الموثق، وبالجملة فيتبع أخس ما فيه من الصفات حيث تتعدد
A narration whose transmission consistently reaches the infallible through an Imami who is praised with acceptable and considerable praise which is uncontested by condemnation, together with that being the case in all the links of the narrators, or at least in some of them. So, for example, when there is one Imami among them who is praised but not trustworthy, with the remaining narrators in the chain being of the level of Sahih, the chain will be graded as Hassan due to that one individual.
They have with the clause ‘the remaining narrators in the chain being of the level of Sahih’ precluded an instance wherein an inferior narrator to him is present, for in that case the narration would be considered lower. As in the instance where there is a weak narrator due to whom the chain will be Da’if¸ or where there is a narrator who is not an upright Imami due to whom it will be Muwaththaq. In essence, the ruling is always subject to the lowest narrator when there are narrators of varying degrees.
So, basically, they agree that the following are the requisites of Hassan:
From this it is understood that all the narrators are not of confirmed uprightness, or some are not whilst others are. Hence, the known principle is that the narration will be subject to the lowest narrator. And if he were to lack in another requisite other than uprightness the narration would not be Hassan.
And the author of Diya’ al Dirayah mentions the following:
ألفاظ المدح على ثلاثة أقسام: ما له دخل في قوة السند، مثل صالح وخير. ما له دخل في قوة المتن لا في السند، مثل فهيم وحافظ. ما ليس له دخل فيهما، مثل شاعر وقارئ. فالأول يفيد في كون السند حسنا أو قويا، والثاني ينفع في مقام الترجيح، والثالث لا عبرة له في المقامين، بل هو من المكملات
The phrases of praise are of three types:
a) Phrases which have a bearing on the strength of the chain, like: Salih (pious) and Khayr (good),
b) Phrases which have a bearing on the strength of the wording not the chain, like: Fahim (understanding) and Hafiz (retainer),
c) Phrases which have no influence on both, like: Sha’ir (poet) and Qari’ (reader). The first type implies that the chain is either Hassan or Qawi, the second is of benefit in the context of giving preference, and the third is not worth consideration in both, and is just from the enhancing factors.
He also says the following about combining praise and criticism:
القدح بغير فساد المذهب قد يجامع المدح لعدم المنافاة بين كونه ممدوحا من جهة، ومقدوحا من جهة أخرى
A criticism of a flaw other than the corruption of creed at times can come together with praise. This is because there is contradiction between him being praiseworthy in one way, and impugned in another.
The influence of the belief of Imamah on this category is clear from the following:
They have defined it as:
هو ما اتصل سنده إلى المعصوم بمن نص الأصحاب على توثيقه، مع فساد عقيدته، بأن كان من أحد الفرق المخالفة للإمامية، وإن كان من الشيعة، مع تحقق ذلك في جميع رواة طريقه، أو بعضهم، مع كون الباقين من رجال الصحيح. وإلا فلو كان في الطريق ضعيف تبع السند الأخس وكان ضعيفا
A narration whose chain consistently reaches the infallible with a narrator whom the scholars have deemed reliable, in spite of his corrupt belief, due to, for example, belonging to a sect which opposes the Imamiyyah, even though he be from the Shia. Together with that, this requirement should be found in all the narrators, or in some of them, whilst the remainder be from the narrators of Sahih. Or else, if a weak narrator features in the chain the ruling will be subject to the lower grade and the narration will be Da’if.
So in essence, they concur upon the following requisites of the a Muwaththaq narration:
The influence of the belief of Imamah here is clear from the following:
توثيق المخالف لا يكفينا، بل الموثق عندهم ضعيف عندنا، والمدار في الموثق إنما هو توثيق أصحابنا
The authentication of the opponent is not sufficient for us, instead the one approbated by them will be weak according to us. The basis in the Muwaththaq narration is upon the approbation of our scholars.
So approbation does not go beyond the Shia circles.
They have defined it as:
هو ما لم يجتمع فيه شرط أحد الأقسام السابقة، بأن اشتمل طريقه على مجروح بالفسق ونحوه، أو على مجهول الحال، أو ما دون ذلك كالوضاع
A narration which does not meet the requirements of the previous types, due to including a narrator impugned of sinning, etc., or an unknown narrator, or even someone lower than that, like a forger.
And ‘Ali Akbar Ghifari mentions:
وقد أوضح ذلك بعض من عاصرناه بأن الضعيف ما لم يدخل في أحد الأقسام السابقة بجرح جميع سلسلة سنده بالجوارح أو بالعقيدة مع عدم مدحه بالجوارح أو بهما معا، أو جرح البعض بأحدها أو بهما، أو جرح البعض بأحد الأمرين مع جرح الآخر بالأمر الأخر أو سواء كان الجرح من جهة التنصيص عليه أو الاجتهاد أو من جهة أصالة عدم أسباب المدح والاعتبار، سواء جعلنا الأصل هو الفسق و الجرح، أو قلنا بأنه لا أصل هناك، ولا فرق في صورة اختصاص الجرح بالبعض بين كون الباقي أو بعض الباقي من أحد أقسام القوي أو الحسن أو الموثق أو الصحيح بل أعلاه لما مر من تبعية الوصف لأخس الأوصاف
This has been clarified by one of our contemporaries; a Da’if narration is one that does not fall under any of the previous types due to all the links of its chain being impugned with various criticisms, or due to a false creed alone, or due to both (false belief and being impugned with criticisms), or due to some of them being impugned with one criticism, or with both, or due to one being impugned with one criticism and the other with another or with both, and so on. Furthermore, it is equal whether the impugning is based on explicit mention thereof (from a prior scholar), or it is based on Ijtihad, or upon the absence of the factors of approbation and consideration. Also, it is equal whether we deem sinning and being impugned to be the primary status, or we say there is no primary status. And there is no difference, in the case where one narrator specifically is impugned, between all the remaining narrators, or some of them, being from the level of Qawi, Hassan, Muwaththaq, Sahih, or its highest level because of what has passed, i.e. the grading will always be subject to the lowest level.
From the aforementioned it is clear that the Rawafid, in their definition of a Sahih narration, considered a non-Jafari to be a Kafir or a Fasiq, owing to which his narration is unacceptable. Likewise, the narration of a non-Jafari narrator will only be accepted if he has been approbated by the Jafariyyah.
Thus, on the basis of these principles, they reject the established narrations of the three Rightly Guided Khalifas, other senior Sahabah, their successors, the leading scholars of hadith and the Jurists, i.e. due to them not believing in the creed of the Twelver Imamiyyah. Hence, narrations in whose chains anyone of these truthful and pious people who were leaders and trustworthy appear are unreliable according to these people who barely understand anything.
 Dirasat fi ‘Ilm al Dirayah (the abridgement of Miqbas al Hidayah) of ‘Ali Akbar Ghifari, p. 18, 19; Nihayah al Dirayah, p. 97.
 Al Usul al ‘Ammah li al Fiqh al Muqaran, p. 195, onwards.
 Minhaj al Sunnah, 1/8
 Dirasat fi ‘Ilm al Dirayah, p. 23; Nihayah al Dirayah, p. 102.
 Buhuth fi Fiqh al Rijal, p. 33; Nihayah al Dirayah, p. 235; Dirasat fi ‘Ilm al Dirayah, p. 26; Sama’ al Maqal, p. 2/422.
 The Rawafid have not abided by this requirement, for their chains of transmission are concocted, inconsistent, and forgeries. For more details refer to the following discussions: ‘the Rawafid and the Asanid’, and ‘the unknown narrators in the books of the Rawafid’ in this book.
 They have also not abided by this, for they have accepted the narrations of the Waqifah, the Nawusiyyah, the Fathiyyah, al Khattabiyyah, etc., all of whom they consider to be disbelievers. Refer to the discussion: ‘the narrators of the Rawafid who have been impugned in their reliable books’.
 This is also something they have not abided by, for they have accepted the narrations of accursed people, liars, imposters, etc. Refer to the discussion: ‘the methodology of authenticating and deeming weak according to the Rawafid’, and also: ‘the status of the Rafidi narrators’.
Furthermore, uprightness is not considered at all by their later scholars due to it not being mentioned in the texts of the early Shia scholars. Al Majlisi says:
ثم اعلم أن المتأخرين من علمائنا اعتبروا في العدالة الملكة، وهي صفة راسخة في النفس تبعث على ملازمة التقوى والمروءة، ولم أجدها في النصوص، ولا في كلام من تقدم على العلامة من علمائنا، ولا وجه لاعتبارها.
Then know that the later scholars have taken Malakah (inherent ability) into consideration in ‘uprightness’; it is a deeply rooted attribute which propels one to always abide by piety and dignity. I have not found this in the early texts, nor in the statements of the scholars who preceded al ‘Allamah, and there is no reason to consider it. Bihar al Anwar, 85/32.
Also, the basis of approbation according to the scholars of the Shia is assumption. Muhammad al Baqir says:
والمدار في التعديل على ظنون المجتهد
The basis of approbation is upon the assumptions of the Mujtahid. Al Fawa’id al Ha’iriyyah, p. 489.
However, Abu al Qasim al Khu’i has opposed him saying:
قد ثبت بالأدلة الأربعة حرمة العمل بالظن
The impermissibility of practicing upon conjecture has been established in the four evidences. Mujam Rijal al Hadith, 1/19, also see: Rijal al Khaqani, p. 11; Kulliyyat fi ‘Ilm al Rijal, p. 21.
 Tahdhib al Wusul ila ‘Ilm al Usul, p. 77, 78.
 Dirasat fi ‘Ilm al Dirayah, p. 28; also see: Buhuth fi Fiqh al Rijal, p. 33; Nihayah al Dirayah, p. 259.
 Diya’ al Dirayah, p. 24.
 Dirasat fi ‘Ilm al Dirayah, p. 30; Buhuth fi Fiqh al Rijal, p. 33; Sama’ al Maqal, p. 443.
 Diya’ al Riwayah, p. 25.
 Dirasat fi ‘Ilm al Dirayah, p. 32; Buhuth fi Fiqh al Rijal, p. 32, 33.
 Ibid. 32, 33.