The Promised Deliverer (Kitab Al-Mahdi)
Dawud :: Book 36 : Hadith 4269
Narrated Abdullah ibn Mas'ud:
The Prophet (peace_be_upon_him) said: If only one day of this world remained. Allah would lengthen that day (according to the version of Za'idah), till He raised up in it a man who belongs to me or to my family whose father's name is the same as my father's, who will fill the earth with equity and justice as it has been filled with oppression and tyranny (according to the version of Fitr). Sufyan's version says: The world will not pass away before the Arabs are ruled by a man of my family whose name will be the same as mine.