Abu’l-Hasan ‘Ali ibn Musa, known as ar-Rida (the approved or acceptable) was born in Medina in 148/765. Various names are given to his mother in the historical sources but what is that she was a slave. He was thirty-five years old when his father died.

It was during the Imamate of ar-Rida that the Caliph Harun ar-Rashid died at the Empire was split between his two sons: Amin, who was born of an Arab mother and controlled Iraq and the West with his Arab vizier al-Fadl ibn Rabi’; and Ma’mun, who was born of a Persian mother and controlled Iran and the East with his Iranian vizier, al-Fadl ibn Sahl. Amin attempted to interfere with the arrangements for the succession that had been agreed upon and soon there was a civil war in which Amin was defeated and Ma’mun’s army under the Iranian General, Tahir, occupied Baghdad. Ma’mun, however, remained for the time being in Marv in Khurasan.

It was at this point that Ma’mun suddenly and somewhat unexpectedly summoned ‘Ali ar-Rida from Medina to join him at Marv. On ar-Rida’s arrival he was appointed, somewhat reluctantly it is said, to be Ma’mun’s heir-apparent.

There has been much conjecture as to what caused Ma’mun to adopt this course of action. Some have suggested that the revolts in the West of the Empire-some of them under a Shi’i banner led by Zaydi Imams-were becoming serious and this was a political move designed to give Ma’mun the support of a body of the Shi’a and a respite. Some have suggested that it was the work of his powerful vizier, al-Fadl ibn Sahl, who had Shi’i proclivities.

It was while ar-Rida was in Marv that his sister, Fatima, known as Ma’suma ( the immaculate) set out from Medina to see him. She died at Qumm en route and it is her shrine which is the religious focus of the city of Qumm. Qumm had been founded as a Shi’i town when, in 94/712, Ahwas ibn Sa’d al- Ash’ari had fled from Kufa as a result of the persecutions of Shi’is being carried out by the Umayyad Governer, al-Hajjaj. The present imposing shrine was constructed mainly by Shah Bigum, the daughter of Shah Isma’il, in 925/1519 and additions were made throughout the Safavid and Qajar eras. Gold tiles were placed on the roof by the Qajar monarch Fath ‘Ali Shah. A number of the most important theological colleges in the Shi’i world have grown up around this shrine.

Whatever may have been the cause of Ma’mun’s nomination of ar-Rida (which occured in the year 201/816) there can be no doubt that it caused a great stir. Everywhere the black standards and uniforms of the ‘Abbasid’s were changed to the green of the ‘Alids. In Iraq, the Abbasid family rebelled and set up a rival Caliph.

In order to quell these rebellions, Ma’mun set out with his court and army towards Iraq. At Tus, in the way to Iraq, ‘Ali ar-Rida suddenly took sick and died. The year was 203/818. The suddenness of his death has caused most writers to state that ha was poisoned and the Shi’i writers accuse the Caliph Ma’mun of doing this out of jealousy for the attention which the people held ar-Rida, but there were other parties, especially the deposed ‘Abbasids, who had reason to hate ar-Rida.