• Name: Muhammad.
• Title: al-Mahdi, al-Qa’im, al-Hujjah, al-Gha’ib, Sahibu’z-Zaman, Sahibu ‘l-Amr.
• Agnomen: Abu ‘l-Qasim.
• Father’s name: al-Hasan al-Askari.
• Mother’s name: Narjis.
• Birth: In Samarra’, on Friday, 15th Sha’ban 255 AH. (He is still living and will appear before the end of the world)
• Minor Occultation: 8th Rabi`u1-awwal 260 AH.
• Major Occultation: 10th Shawwal 329 AH.

There existed a good deal of harmony and uniformity between the aspects pertaining to the births of Prophet Muhammad, the last Apostle of Allah and Imam al-Mahdi, the last Apostolic Imam. Just as the coming of the Holy Prophet was prophesied well in advance by the preceding prophets, similarly the impending news of the gracious birth of Imam al-Mahdi was foretold by the Holy Prophet.

Innumerable traditions in this context, quoted right from the Holy Prophet, from the glowing contents of many books of Masanid, Sihah and Akhbar, and of Shiite scholars (ulama’) existed. Many Sunni scholars have accumulated these traditions in complete volumes also, e.g.: al-Bayan fi akhbar Sahibi’z-Zaman by al-Hafiz Muhammad ibn Yusuf ash-Shafi’i and Dhikriyyatu’l-Mahdi by al-Hafiz Abu Nu’aym alIsfahani as well as as-Sahih of Abu Dawud and as-Sunan of Ibn Majah. All of the above books record the traditions bearing evidence of the coming of this Holy Imam.

The promised Mahdi, who is usually mentioned by his title of Imamu’l-`Asr (the Imam of the Period) and Sahibu’z-Zaman (the Lord of the Age), is the son of the Eleventh Imam. His name is the same as that of the Holy Prophet. He was born in Samarra’ in 255/869 and until 260/874 when his father was martyred, lived under his father’s care and tutelage. He was hidden from public view and only a few of the elite among the Shi’ah were able to meet him.

After the martyrdom of his father he became Imam and by Divine Command went into occultation (ghaybah). Thereafter, he appeared only to his deputies (na’ib) and even then only in exceptional circumstances.

The Imam chose as a special deputy for a time Uthman ibn Said al-Amri, one of the companions of his father and grandfather who was his confident and trusted friend. Through his deputy the Imam would answer the demands and questions of the Shi’ah. After Uthman ibn Said, his son Muhammad ibn Uthman al-Amri was appointed the deputy of the Imam, After the death of Muhammad ibn Uthman, Abu’l-Qasim al-Husayn ibn Ruh an-Nawbakhti was the special deputy, and after his death Ali ibn Muhammad as-Samuri was chosen for this task.

A few days before the death of Ali ibn Muhammad as-Samuri in 329/939 an order was issued by the Imam stating that in six days `Ali ibn Muhammad as-Samuri would die. Henceforth the special deputation of the Imam would come to an end and the major occultation (ghaybatu’1-kubra) would begin and would continue until the day God grants permission to the Imam to manifest himself.

The occultation of the Twelfth Imam is, therefore, divided into two parts: the first, the minor occultation (ghaybatu’s-sughra) which began in 260/872 and ended in 329/939, lasting about seventy years; the second, the major occultation which commenced in 329/939 and will continue as long as God wills it. In a hadith upon whose authenticity everyone agrees, the Holy Prophet has said, “If there were to remain in the life of the world but one day, God would prolong that day until He sends in it a man from my community and my household. His name will be the same as my name. He will fill the earth with equity and justice as it was filled with oppression and tyranny.”

Al-Imam al-Hujjah, peace be on him, said:

“Rest assured that no one has a special relationship with Allah. Whoever denies me is not my (follower). The appearance of the Relief (al-faraj) depends solely upon Allah; therefore, those who propose a certain time for it are liars. As to the benefit of my existence in Occultation, it is like the benefit of the sun behind clouds where the eyes do not see. Indeed, my existence is an amnesty for the people of the earth. Pray much to Allah to hasten the Relief, for therein also lies the release from your sufferings.”

Reference: https://www.al-islam.org/brief-history-fourteen-infallibles/fourteenth-infallible-twelfth-imam