The promised Al Mahdi, who is usually mentioned by his title Sahib al-Zaman (the Lord if the Age), is the son of the eleventh Imam. His name is the same as that of the Holy Prophet, Muhammad. Muhammad Ibn Hasan. He was born is Samarrah, Madinah. On the 14th of Sya’ban 255 AH, after iftihaar, the 11th Imam (Imam Hasan Askari A.S.) informed th people in his house that his son was to be born soon. There was no sign of pregnancy on Sayyida Narqisy (the Imam Hasan Askari wife).
At the time of fajr on 15th Syaban, people in the house (which was Imam Hasan Askari A.S, her wife Sayyida Narqisy, and Sayyida Hakima – the sister of the 10th Imam, Imam Muhammad Taqi Al-Javad A.S.) heard that the Suratul Qadar being recited from the womb of sayyida Narqisy. The 11th Imam told them that the birth would occur very soon. As soon as the 12th and the last Imam was born, he did sidja and proclaimed the onesess of ALLAH and the Prophet hood of the Prophet (S.A.W.).He also recited the 5th aya of Suratul Qasas. On his right hand has written the 82nd aya of Suratul Bani Israil. The 11th Imam only told a handful of his most trusted bellievers f the birth of his son and to a few of his household slaves.
His name is the same as the name of The Prophet (S.A.W.), i.e. Muhammad. For those who believe, the last Imam was hidden from public view and only a few of saint people were able to meet him. After the martyrdom of his father he became Imam and by Divine Command went into occulation (ghaibat). Ghaibat menas that he is hidden by ALLAH from the eyes of the people, but the people are not hidden from his eyes. Theareafter he comes during Hajj and appeared only to his deputies (na’ib) and even then only in exceptional circumtances/majlisy.
And once again, for those who believe, these are the hadith about the appearance of Imam Mahdi :
The Prophet (S.A.W.) said : “ even if entire duration of the wolrds’s existence has already been exhausted and only one day is left (before the day of judgement), ALLAH will expand that day to such a length of time, as to accomodate the kingdom of a person from my Ahlul-Bayt who will be called by my name. He will fill out the earth with peace and justice as it will have been full of injustice and tirany. (Shahih al-Thirmidzi. Vol 2, Page 86., Vol. 9, Page 74-75., Sunan Abu Dawud. Vol.2 Page 7., Musnad Ahmad Ibn Hanbak, Vol.1, Page 84)
The Prophet (S.A.W.) said : Al Mahdi will be from my progeny. His forehead will be broad and his nose will be high. He will fill the world with justice and fairness at a time when the world will be filled with oppression. He will rule for seven years. (Hazrat Abu Saeed Khudri R.A Vol.2, Page 208., Fusul Al-Muhimma Page 275)
Yaa Washi al Hasani wal Kholafal Hujjah, ayyuhal Qoimul Muntazaral Mahdy, yabna Rasulillah, Yaa Hujjatallahi ‘Ala kholqih, Yaa sayyidanaa wa maulaanaa, inna tawajjahnaa wastasyfa’naa watawasalnaa bika ilALLAH, wa qodamnaaka bayna yadayhaajaatinaa, yaa Wajiihan ‘indaLLAH, isyfa’lanaa ‘indaLLAH.