Silsilah as-Sahihah 3635 — Story of Imam Mahdi

It is narrated from Sayyiduna Ali (may Allah be pleased with him), the Messenger of Allah (peace and blessings of Allah be upon him) said: "The Mahdi will be from us, that is, from the Ahl al-Bayt. Allah Almighty will set his affairs right in a single night."