أن رسول الله صلى الله عليه وسلم قال لعلي قبل موته: تبرئ ذمتي، وتقتل على سنتي.
Indeed, the Messenger of Allah salla Llahu ‘alayhi wa sallam said to ‘Ali before his death, “You will discharge my responsibility (i.e. of conveying the Message) and you will be murdered on my Sunnah.”
This hadith is narrated by Abu Rafi’, Ibn ‘Umar, and ‘Ali radiya Llahu ‘anhum.
The Hadith of Abu Rafi’
Al Bazzar and Ya’qub al Fasawi narrate — from Muhammad ibn ‘Ubaidullah ibn Abi Rafi’ — from his father — from Abu Rafi’.
Muhammad ibn ‘Ubaidullah ibn Abi Rafi’ is matruk (suspected of forgery).
The Hadith of Ibn ‘Umar
Ibn al Maghazili narrates from — Hussain ibn Nasr ibn Muzahim — Khalid ibn ‘Isa al ‘Ukli narrated to us — Hussain ibn Mukhariq narrated to us — Jafar ibn Muhammad narrated to us — from his father — from Nafi’, the mawla (freed slave) of Ibn ‘Umar who said to Ibn ‘Umar, “Who is the best person after the Messenger of Allah salla Llahu ‘alayhi wa sallam?” He said, “What is with you and this question? May your mother bereave you!” Then he said, “Astaghfir Allah; the best person after the Messenger of Allah salla Llahu ‘alayhi wa sallam is a person that enjoys the same status of halal and haram as Nabi salla Llahu ‘alayhi wa sallam (i.e. whatever is was made halal and haram for Nabi salla Llahu ‘alayhi wa sallam is also halal and haram for him).” I said, “Who is such a person?” He said, “‘Ali; the doors of the masjid were ordered to be closed, and ‘Ali’s door was left open. The Messenger of Allah salla Llahu ‘alayhi wa sallam said to him, ‘You are permitted to do whatever I am permitted to do in this masjid and you are to observe whatever I am to observe in this masjid. You are my warith (inheritor) and my wasi (executor) who will fulfill (the obligations of) my Din. You will deliver the deathblow to my enemies and you will be murdered on my Sunnah. Whoever claims to hate you and love me (at the same time) is a liar.’”
Al Daraqutni regarded Hussain ibn Mukhariq as a kadhdhab (liar).
The narrators Hussain ibn Nasr ibn Mazahim and Khalid ibn ‘Isa al ‘Ukli could not be traced.
The Hadith of ‘Ali
As mentioned previously, this hadith is narrated by al Hakim — from Hayyan al Asadi, who heard ‘Ali saying, “The Messenger of Allah salla Llahu ‘alayhi wa sallam said to me, ‘Indeed, the Ummah will act perfidiously with you after me. And you will live on my millah (tradition). And you will be killed on my Sunnah. Whoever loves you, loves me. And whoever hates you, hates me. And indeed this (i.e. his beard) will soon be stained from this (i.e. from his head).’”
As I have mentioned previously, the hadith is da’if (weak).
Ibn ‘Adi narrates with a chain of transmission that contains the narrators Yahya ibn ‘Abdullah al Raqi, Yunus ibn Abi Ya’qub and Ziyad ibn Abi Ziyad al Asadi. They could not be traced.
‘Ali ibn Nizar is worthless (laysa bi shayʾin).
In short, all the chains of transmission are wah (feeble), except for one of the two versions of ‘Ali, it is da’if (weak). Therefore, the hadith is da’if (weak).
 Al Bazzar: Musnad al Bazzar, hadith no. 3873; Ya’qub al Fasawi: Mashyakhah Ya’qub ibn Sufyan al Fasawi, hadith no. 53.
 Ibn al Maghazili: Manaqib ‘Ali, hadith no. 309.
 Al Hakim: Mustadrak al Hakim, hadith no. 4686.