In the last months of the prophet's life, Gabriel descended to the prophet conveying a message from Allah: "There remain two obligations that you must convey to your people: the obligation of Hajj, and the obligation of Wilayah (the guardianship and succession) after you. For indeed, I have never left My earth without a proof, and I will never leave it without one." The Prophet had often spoken about Imam Ali's unique rank, but hadn't formalized his succession in front of a large audience.