Musnad Ahmad 907:13

Hammad ibn Usamah narrated to us, Mujalid narrated to us, from Amir, from Jabir ibn Samurah al-Suwa'i, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying during the Farewell Pilgrimage: "Indeed, this religion will not cease to be manifest over those who oppose it; it will not be harmed by those who differ with it, nor by those who separate from it, until twelve caliphs from my nation have passed." He said: Then he spoke something I did not understand. So I said to my father: "What did he say?" He said: "All of them are from Quraysh."