Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that the Messenger of Allah (peace and blessings be upon him) said to Sayyidah Umm Salamah (may Allah be pleased with her): "This is Ali bin Abi Talib; his flesh is my flesh and his blood is my blood. His position in relation to me is that of Harun (peace be upon him) in relation to Musa (peace be upon him), except that there is no prophet after me."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12289