Musa al-Kazim in the context of "Raj'a"

Ismailism, known historically and among practitioners as Esotericism, is a branch of Shia Islam. Like all Shia, the Ismailis emphasize a distinction between the exoteric (zahir) and esoteric (batin) dimension of Islam, and hold that the esoteric meaning was preserved from corruption by a line of descendants of Muhammad (imams). However, unlike other Shia, the Ismaili are characterized by a unique emphasis on the esoteric that approaches antinomianism.

The Isma'ili (/ˌɪzmɑːˈɪliː/) get their name from their acceptance of Imam Isma'il ibn Jafar as the appointed spiritual successor (imām) to Ja'far al-Sadiq, wherein they differ from the Twelver Shia, who accept Musa al-Kazim, the younger brother of Isma'il, as the true Imām.

Ali ibn Musa al-Rida (Arabic: عَلِيّ ٱبْن مُوسَىٰ ٱلرِّضَا, romanized: ʿAlī ibn Mūsā al-Riḍā, c. 1 January 766 – c. 6 June 818), 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 in 799 CE. 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-Risalah al-Dhahabiah, Sahifah of al-Ridha, and Fiqh al-Rida. Uyoun Akhbar Al-Ridha 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.

Al-Rida was contemporary with the Abbasid caliphs Harun al-Rashid (r. 786–809) and his sons, al-Amin (r. 809–813) and al-Ma'mun (r. 813–833). In a sudden departure from the established anti-Shia policy of the Abbasids, possibly to mitigate the frequent Shia revolts, al-Mamun invited al-Rida to Merv in Khorasan, his de facto capital, and designated him as heir apparent, despite the reluctance of the al-Rida who accepted the offer on the condition that he would not interfere in governmental affairs. The appointment of Ali al-Rida by the Abbasid al-Mamun immediately invoked strong opposition, particularly among the Abbasids, who revolted and installed Ibrahim ibn al-Mahdi, a half-brother of Harun al-Rashid, as the anti-caliph in Baghdad. Realising the severity of the Iraqi opposition, al-Mamun and his entourage left Khorasan for Baghdad, accompanied by al-Rida. The Imam, however, died mysteriously when the party reached Tus in September 818. His death followed shortly after the assassination of al-Fadl ibn Sahl, the Persian vizier of al-Mamun, who was publicly seen as responsible for his pro-Shia policies. The caliph is often seen as responsible for both deaths, as he made concessions to the Arab party to smooth his return to Baghdad. Tus was later replaced with a new city, called Mashhad, which developed around the grave of al-Rida as the holiest site in Iran, to which millions of Shia Muslims flock annually for pilgrimage.

Muhammad ibn Isma'il al-Maktum (Arabic: مُحَمَّد ٱبْن إسْماعِيل ٱلْمَكتُوم, romanized: Muḥammad ibn Ismāʿīl al-Maktūm; c. 740–813) was the eldest son of Isma'il al-Mubarak and the seventh imam in Isma'ilism. When Isma'il died, his son Muhammad continued to live in Medina under the care of his grandfather Ja'far al-Sadiq until the latter's death in 148/765. After the death of Abd Allah al-Aftah, Muhammad was the most senior member of the Husaynid branch of the Alids. However, due to the rival group that recognised Musa al-Kazim as their imam, and the Abbasid Caliphate's persecution of all Alid partisans, Muhammad fled Medina with his sons for the east. For this reason, he was known as al-Maktum (lit. 'the hidden one'). He had two sons when living in Medina and then four more sons after his emigration, among whom was his successor Ahmad al-Wafi. Muhammad's descendants became the Fatimid dynasty that ruled Ifriqiya and later Egypt and much of the Levant, and founded Cairo.

Ali ibn Musa al-Rida (Arabic: علي بن موسى الرضا, romanized: ʿAlī ibn Mūsā al-Riḍā, c. 1 January 766 – c. 6 June 818), 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 in 799 CE. 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-Risalah al-Dhahabiah, Sahifah of al-Ridha, and Fiqh al-Rida. Uyoun Akhbar Al-Ridha 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.

Al-Rida was contemporary with the Abbasid caliphs Harun al-Rashid (r. 786–809) and his sons, al-Amin (r. 809–813) and al-Ma'mun (r. 813–833). In a sudden departure from the established anti-Shia policy of the Abbasids, possibly to mitigate the frequent Shia revolts, al-Mamun invited al-Rida to Merv in Khorasan, his de facto capital, and designated him as heir apparent, despite the reluctance of the al-Rida who accepted the offer on the condition that he would not interfere in governmental affairs. The appointment of Ali al-Rida by the Abbasid al-Mamun immediately invoked strong opposition, particularly among the Abbasids, who revolted and installed Ibrahim ibn al-Mahdi, a half-brother of Harun al-Rashid, as the anti-caliph in Baghdad. Realising the severity of the Iraqi opposition, al-Mamun and his entourage left Khorasan for Baghdad, accompanied by al-Rida. The Imam, however, died mysteriously when the party reached Tus in September 818. His death followed shortly after the assassination of al-Fadl ibn Sahl, the Persian vizier of al-Mamun, who was publicly seen as responsible for his pro-Shia policies. The caliph is often seen as responsible for both deaths, as he made concessions to the Arab party to smooth his return to Baghdad. Tus was later replaced with a new city, called Mashhad, which developed around the grave of al-Rida as the holiest site in Iran, to which millions of Shia Muslims flock annually for pilgrimage.