The marital relations of Ahlul Bayt, specifically the progeny of Amir al Mu’minin ‘Ali radiya Llahu ‘anhu, was not just restricted to the Sahabah and their progenies, as mentioned above; but we find that they also married [later on] into the progenies of their cousins from the Abbasids. Hereunder we will mention a few of such unions.
Muhammad al Jawwad—considered to be the ninth infallible Imam by the Shia—married Umm al Fadl, the daughter of the Abbasid Khalifah Ma’mun ibn Harun (al Rashid). This marriage took place in the year 202 A.H towards the end of Safar. A number of scholars have recorded this in their books, with a slight difference in her name.
Al Tusturi says:
We did not find but Umm Fadl ibn Ma’mun mentioned. Al Qummi reports from al Rayyan bin Shabib that after the marriage Ma’mun instructed that everybody be seated according to their rank. It was not long before we heard voices sounding like navigators on ships, and then all of sudden their appeared before us a number of servants pulling a ship made of silver, the ropes made from the finest silk, on wheels filled with perfume.
Ma’mun then ordered the nobles to apply Henna from that special perfume. Thereafter, it was taken before the commoners so they too could perfume themselves. The tables were then laid, and people ate… then Ma’mun gave an order and a host of notes were sprinkled over Abu Jafar ‘alayh al Salam, which contained titles to lands, quarries, and workshops.
Sheikh ‘Abbas al Qummi said:
Imam (al Jawwad) ‘alayh al Salam did not have any children from Umm al Fadl.
‘Ali al Rida—considered to be the eighth infallible Imam by the Shia—married Umm Habibah, the daughter of the Abbasid Khalifah Ma’mun ibn Harun (al Rashid). This has been mentioned in a number of references, and it is well-known that not only did Ma’mun make al Rida his son-in-law but also declared him his successor.
‘Abbas al Qummi writes:
He married one of his daughters, Umm Habib, to Imam al Rida ‘alayh al Salam, and proposed one of his daughters for Imam Muhammad al Taqi [al Jawwad]. Ishaq ibn Musa married the daughter of his paternal uncle, Ishaq ibn Jafar. He was then appointed and led the Hajj that year.
The grandson of ‘Umar al Atraf—son of Amir al Mu’minin ‘Ali radiya Llahu ‘anhu—married the paternal aunt of the Abbasid Khalifah Abu Jafar al Mansur.
He also married Zainab bint Khalid ibn Muhammad al Baqir.
The granddaughter of ‘Abdullah al Mahd—grandson of Sayyidina Hassan radiya Llahu ‘anhu—was married to the nephew of the Abbasid Khalifah Abu Jafar al Mansur.
The researcher of ‘Umdat al Talib says, quoting al Majdi of Abu al Hassan al ‘Umari:
The children of Musa ibn ‘Abdullah, titled al Jawn, are 12: 9 daughters… Umm Kulthum. Ibn Dinar said she was married to the nephew of al Mansur.
Mus’ab al Zubari writes:
The children of ‘Abdullah ibn Hussain ibn ‘Ali ibn Hussain ibn ‘Ali ibn Abi Talib: Bakr, Qasim, Umm Salamah, Zainab, who was married to Amir al Mu’minin Harun. He divorced her after one night, and as a result the people of Madinah referred to her as Zainab Laylah. Their mother was an Umm Walad Nuwaybah.
The entire incident can be read in Jamharat Ansab al ‘Arab, under the children of Hussain ibn ‘Ali ibn Hussain ibn ‘Ali ibn Abi Talib.
The daughter of Muhammad Dhu Nafs al Zakiyyah, great grandson of Sayyidina Hassan radiya Llahu ‘anhu, was married to the Abbasid Khalifah Muhammad ibn Abi al ‘Abbas.
Ibn Habib says:
The daughter of Muhammad ibn ‘Abdullah ibn Hassan ibn Hassan was married to Muhammad ibn Abi al ‘Abbas Amir al Mu’minin. He consummated the marriage in Madinah after her father was killed, and then divorced her in the morning. She was then married by ‘Isa ibn ‘Ali, and then by Muhammad ibn Ibrahim al Imam, then by Hassan ibn Ibrahim ibn ‘Abdullah ibn Hassan. They said that Hassan ibn Ibrahim actually married her sister.
Ibn Hazm said:
From the children of Hussain ibn Zaid ibn ‘Ali ibn Hussain ibn ‘Ali ibn Abi Talib: Hassan, Hassan, ‘Ali, Jafar, ‘Abdullah, Muhammad, Ishaq, Zaid, Yahya, and Maimunah, who married Amir al Mu’minin al Mahdi, the Abbasid Khalifah.
Ibn Qutaybah says:
As for Hussain ibn Zaid, he went blind. His daughter was married to al Mahdi, for whom she bore a child.
 The lineage of the Abbasid Khalifas goes back to Sayyidina ‘Abbas ibn ‘Abdul Muttalib radiya Llahu ‘anhu, uncle of the Prophet salla Llahu ‘alayhi wa sallam.
 The scholars are in disagreement concerning the name of Ma’mun’s daughter who married Muhammad al Jawwad; whether it was Umm al Fadl or Umm Habib.
 Tawarikh al Nabi wa al Al, pg. 111, Dar al Sharafah.
 Muntaha al Amal, 2/569, Mu’assat al Nashr.
 Muntaha al Amal, 2/373, Maktabah al Fikr; the Mu’assat al Nashr edition has profuse errors in this section.
 ‘Umdat al Talib, pg. 134, Dar al Hayat, pg. 103, Ansariyan)
 Nasab Qurasyh, pg. 73.
 Al Muhabbar, pg. 449, 450.
 Jamharat Ansab al ‘Arab, children of Hussain ibn Zaid.
 Al Ma’arif, pg. 216.