Abu Layla al-Hadrami narrates from Sayyiduna Zayd bin Arqam (may Allah be pleased with him); he said: The Messenger of Allah (peace and blessings be upon him) came out to us and said: "Do I not have a greater right over you than you have over yourselves?" The Companions said: Indeed, yes. He said: "Then whoever I am the mawla of, Ali is his mawla."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5049