Until their deaths, the tenth and eleventh of the
Twelve Imams were held under close surveillance in the garrison town of
Samarra by the
Abbasids, who are often responsible in Shia sources for poisoning the two Imams, namely,
Ali al-Hadi and Hasan al-Askari. Contemporary to the tenth Imam, the Abbasid
al-Mutawakkil heavily persecuted the Shia, partly due to a renewed
Zaydi opposition. The restrictive policies of al-Mutawakkil towards the tenth Imam were later adopted by his son,
al-Mu'tamid, who is reported to have kept the eleventh Imam under house arrest without any visitors. Instead, al-Askari is known to have mainly communicated with his followers through a network of representatives. Among them was
Uthman ibn Sa'id, who is said to have disguised himself as a seller of cooking fat to avoid the Abbasid officers.
Tabatabai suggests that these restrictions were placed on al-Askari because the caliphate had come to know about traditions among the Shia elite, predicting that the eleventh Imam would father the eschatological
Mahdi.
Death of al-Askari Al-Askari died in 260 (873–874) without an obvious heir. Immediately after the death of the eleventh Imam, his main representative, Uthman ibn Sa'id, claimed that the Imam had an infant son, named Muhammad. This infant was kept hidden from the public out of fear of Abbasid persecution, who sought to eliminate an expected child of al-Askari, whom persistent rumors described as a savior. Uthman also claimed that he had been appointed to represent the son of al-Askari, who is more commonly known as Muhammad al-Mahdi (). Being the closest associate of al-Askari, Uthman's assertions were largely accepted by other representatives of al-Askari. Those followers who accepted the imamate of this Muhammad later formed the Twelvers. The other sects created over the succession of al-Askari disappeared within a hundred years.
Occultation Thus began a period of about seventy years, later termed the
Minor Occultation (, 260-329 AH, 874–941 CE), during which it is believed that four successive agents represented Muhammad al-Mahdi, the Hidden Imam, starting with Uthman ibn Sa'id as the first agent. The fourth agent,
Abu al-Hasan al-Samarri, is said to have received a
letter from Muhammad al-Mahdi shortly before his death in 941 CE. The letter predicted the death of al-Samarri in six days and announced the beginning of the complete occultation, later called the
Major Occultation, which continues to this day. The letter, ascribed to al-Mahdi, added that the complete occultation would continue until God permitted him to manifest himself again in a time when the earth would be filled with tyranny. In Twelver belief, the life of al-Mahdi has been miraculously prolonged. Al-Mahdi is also viewed responsible for the affairs of men and, in particular, their inward spiritual guidance during the occultation. == Career of al-Mahdi ==