Musnad Abu Ya'la al-Mawsili 3:205

Abu Bakr ibn Abi Shaybah narrated to us, Abu Dawud ‘Umar ibn Sa‘d narrated to us, from Yasin, from Ibrahim ibn Muhammad, from his father, from ‘Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Mahdi is from us, the People of the House; Allah will rectify him in a single night."