Imam Muhammad Taqi (as) said to Abdulazim Hasani (as): "Qaim is the promised Hazrat Mahdi (as). He must be awaited when absent and obeyed when he comes...
I swear to Allah Who choose the Prophet Muhammad (saas) that even if one day remains until Doomsday, Allah will send Hazrat Mahdi (as) and prolong that day so that he can fill the world that is full of oppression with justice instead. HE WILL ORDER HIS RULE, AS WITH THE RULE OF THE PROPHET MUSA (AS), IN ONE DAY. Musa (as) went to collect fire for his wife. But returned with the office of a messenger and prophet." (Imam Muhammad Taqi) (Bihar Al-Anwar, Vol. 51, p. 156; Ithbat Al-Hudat, Vol. 6, p. 420)
(The imam narrates five hadith on this subject.)