Riyah bin al-Harith al-Nakha'i (may Allah have mercy on him) narrates: We were sitting with Sayyiduna Ali (may Allah be pleased with him) when some riders of the Ansar came, wearing turbans. They said: Peace be upon you, O our mawla! Sayyiduna Ali (may Allah be pleased with him) said: Am I your mawla, while you are an Arab people? They said: Yes, we heard the Prophet (peace and blessings be upon him) say: "Whoever I am the mawla of, Ali is his mawla. O Allah, befriend whoever befriends him and be hostile to whoever is hostile to him." And here is Abu Ayyub among us. So Abu Ayyub (may Allah be pleased with him) removed the turban from his face and said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever I am the mawla of, Ali is his mawla. O Allah, befriend whoever befriends him and be hostile to whoever is hostile to him."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4038