Musnad Abu Ya'la al-Mawsili 105:49

Abu Bakr ibn Abi Shaybah narrated to us, Muhammad ibn Abdullah al-Asadi narrated to us, from Isra'il, from Simak, from Tharwan ibn Milhan, who said: We were sitting in the mosque when Ammar passed by us. We said to him, "Narrate to us a hadith of the Messenger of Allah (peace and blessings of Allah be upon him) regarding the tribulation (fitnah)." He said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "There will be, after me, leaders who will fight one another for the kingdom; some of them will kill others for it." We said: "If anyone other than you had narrated it to us, we would have called him a liar. As for it, it will surely be..."