Numerous traditions are quoted from the Prophet of Islam that prophesize the advent of His Eminence, Imam Mahdi (a.s):
a. Huzaifah has narrated from the Messenger of Allah (a.s) that he said, “If only a single day remains from the tenure of this world, the Almighty Allah in that same day, will raise a person from my descendants whose name and manners shall be like mine and his patronymic shall be Abdullah, and people would pay allegiance to him between Rukn and Maqam and the Almighty Allah will revive the religion through him and give him victories and all the people on the earth shall be the reciters of the formula ‘La ilaaha Illallaah’ (There is no God except Allah).”
Salman asked: O Allah's Messenger, which of your sons ?
The Holy Prophet (a.s) said, “This son of mine. So saying, he placed his hand on Husain (a.s).”
This tradition means that the reappearance and advent of His Eminence, Imam Mahdi (a.s) is from the confirmed and certain matters that it will indeed come to pass even if a single day remains for the world to end.
 Iqdud Durar, Chapter 2, Tradition 41