Ali ibn Musa al-Rida, also known as Abū al-Ḥasan al-Thānī, was a descendant of the Islamic prophet Muhammad, and the eighth imam in Twelver Shia Islam, succeeding his father, Musa al-Kazim. He is also part of the chain of mystical authority in Sunni Sufi orders. He was known for his piety and learning, and a number of works are attributed to him, including Al-Risala al-Dhahabia, Sahifa al-Rida, and Fiqh al-Rida. Uyun al-Akhbar al-Rida by Ibn Babawayh is a comprehensive collection that includes his religious debates and sayings, biographical details, and even the miracles which have occurred at his tomb. He is buried in Mashad, Iran, site of a large shrine.

Musa ibn Ja'far al-Kazim was a descendant of the Islamic prophet Muhammad and the seventh imam in Twelver Shia Islam. Musa is often known by the title al-Kazim, apparently a reference to his patience and mild demeanor. He was born in 745 CE in Medina to Ja'far al-Sadiq, the sixth Shia imam, who died in 765 without publicly designating a successor to save his heir from the wrath of the Abbasid caliphs. The subsequent crisis of succession was eventually resolved in favor of al-Kazim, with a dissenting group, now known as the Isma'ilis, separating from the mainstream Shia.