It is narrated from Sayyiduna Hubshi bin Junadah (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings be upon him) say on the day of Ghadir Khumm: "O Allah, whoever I am the mawla (patron and friend) of, Ali is his mawla. O Allah, befriend whoever befriends him, be hostile to whoever is hostile to him, help whoever helps him, and assist whoever assists him."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3501