Is Imam Mahdi hiding in the Sardāb (cellar) now?
After five years of living under the care and supervision of his honorable father (Imam Ḥasan al-ˈAskari) and precious mother (Lady Narjis) and following his father’s martyrdom on the 8th of Rabī' al-Awwal in 260 A.H. (5th January 874 A.D.), Imam Mahdi reached the position of Imamate at the age of five just as Prophet Jesus and Prophet John attained the rank of Prophethood in their childhood. Immediately after offering the funeral prayer on the dead body of his father, Imam Mahdi entered the house and no one saw him again among the people since then; this was the beginning of the Imam’s disappearance. It is, however, worth mentioning that, since the Imam used to live secretly in the first five years of his life and the majority of people had no possibility of seeing him, some have calculated the beginning of his occultation from his birthday.[1]
It is necessary to explain that in the house, where Imam Mahdi spent some time and then went into hiding, there was a cool place, namely Sardāb (cellar) to which the people of the house used to take refuge on hot days. Some opponents of Shiˈa have claimed that Shiˈas consider this Sardāb (cellar) to be sacred because they believe that Imam Mahdi is hiding there and will expectedly appear from there at the End of the Time. The truth is that Shiˈas respect this house and its cellar because three Imams- Imam al-Hādi (the tenth Imam), Imam al-ˈAskari, and Imam al-Mahdi- used to live and worship God there for a while. It is routine in almost all religions that the believers, due to their love and affection for the religious leaders, may respect all things belonging or attributed to the sacred leaders. The truth is that the story of Imam Mahdi’s hiding and living in the cellar, as well as his emergence from this place is a false accusation unjustly ascribed to Shiˈa as none of Shiˈite scholars has had such a belief. Beyond that, the Islamic narrations have not mentioned a certain place for the Imam’s life during his occultation except that the promised Mahdi will arise from the side of the Kaˈbah.
Source: Mahdism.net
Derived from the book, Mahdism (In the View of Shiˈa)
[1] Al-Irshād, by Sheikh al-Mufīd, vol. 2, p. 340