Prophet Muhammad (s.a.w) said,"Al-Mahdi is of my progeny from the sons of Fatimah Zahra (s.a)." In every time, there is a need for an Imam. It is necessary for all to know him, believe in his Imamate and it is obligatory for every Muslim to follow him. He represents all the Holy Imams (a.s). Imam Ali (a.s) said, "You are ordained to recognize the Imams (the right successors of the Holy Prophet) and to obey them."