Some old sources did not talk about the birth date of Imam al-Mahdi (a), taking it to be a secret. However, many Shiite and some Sunni hadiths take the year of the Twelfth Shiite Imam (a) to be 255/869 or 256/870. There is also a disagreement about the month in which the Imam (a) was born. Some Shiite and Sunni sources take it to Ramadan, and some Sunni sources take it to be Rabi' I or Rabi' II. However, the majority of scholars take it to be Sha'ban as is evidenced by many old Shiite sources. In historical sources, there are different accounts of the day on which the Twelfth Imam (a) was born, the best-known of which is Sha'ban 15th. Historians who talked about the issue agree that Imam al-Mahdi (a) was born in the house of his father, Imam al-Hasan al-'Askari (a), in Samarra. The house is now part of the shrine of Imam al-Hadi (a) and Imam al-'Askari (a).
Abbasid caliphs knew from the hadiths by the Prophet (s) and the Imams (a) that the Twelfth Imam was al-Mahdi, and thus, they assigned some guards to monitor Imam al-Hasan al-'Askari (a) and his house. According to historians, al-Mu'tamid al-'Abbasi had ordered the midwives to drop by sayyids' houses, especially the house of Imam al-Hasan al-'Askari (a), search inside the house, learn about his wife, and report him about it.
The birth of Imam al-Mahdi (a) was hidden from people. The secrecy of his birth and its reasons are mentioned in some hadiths. According to a hadith from Imam al-Sajjad (a), "our al-Qa'im bears some traditions of the prophets. The tradition from Abraham (a) is the secrecy of his birth and his isolation from the people".
After Imam al-Mahdi's (a) birth, some Shi'as who were close and reliable companions of Imam al-Hasan al-'Askari (a) saw Imam al-Mahdi (a). For example, Imam al-'Askari (a) showed his son to Muhammad b. 'Uthman al-'Amri and 40 other people in his house and said, "this is your Imam after me and my successor among you. Obey him and do not dispute about your religion. Otherwise, you will be disorganized and you will never see him again". Imam al-Mahdi (a) was also seen by people from Banu al-Rahba family from Nusaybin, Banu Sa'id, Banu Mahziyar from Ahvaz, Banu l-Rukuli from Kufa, Banu Nawbakht from Baghdad, and a group of people from Qazvin, Qom, and Jibal. Read more...