Musnad Ahmad 765:2

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Isma'il ibn Abi Khalid, who said: I heard Qays ibn Abi Hazim say: I heard al-Sanabihi al-Bajali say: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "I am your forerunner at the Basin (al-Hawd), and I will boast of your great numbers before the nations." Shu'bah said: Or he said: "before the people." "So do not fight one another after me."