[16] 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.
[17] Immediately after the death of al-Askari in 260 AH (874 CE),[18] Uthman ibn Sa'id claimed that the eleventh Imam had a young son, named Muhammad, who had entered a state of occultation (ghayba) due to the Abbasid threat to his life.
[21] Twelver sources detail that Muhammad al-Mahdi made his only public appearance to lead the funeral prayer for his father instead of his uncle, Ja'far.
[22][23] Thus began a period of about seventy years, later termed the Minor Occultation (al-ghaybat al-sughra, 260-329 AH, 874–940 CE), during which it is believed that four successive agents acted as intermediaries between the Hidden Imam and his followers.
[29] The letter, ascribed to al-Mahdi, added that the complete occultation would continue until God granted him permission to manifest himself again in a time when the earth would be filled with tyranny.
[31] Ibn Babawayh (d. 991) and Tusi (d. 1067) both quote this final letter, parts of which are presented below:O' Ali b. Muhammad al-Samarri, may God reward your brethren in your death, which is going to take place in six days' time.