Abu Salman the mu'adhdhin narrates from Sayyiduna Zayd bin Arqam (may Allah be pleased with him); he said: Sayyiduna Ali (may Allah be pleased with him) adjured the people: "I ask, by Allah, has anyone heard the Prophet (peace and blessings be upon him) say: 'Whoever I am the mawla (patron) of, Ali is his mawla. O Allah! Befriend whoever befriends him, and be hostile to whoever is hostile to him'?" Twelve Companions who had fought at Badr stood up and testified to it. Sayyiduna Zayd (may Allah be pleased with him) says: And I too was among those who concealed (the testimony), and my eyesight was lost.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4977