Musnad Ahmad 765:1

Yahya ibn Sa'id and Waki' narrated to us, they said: Isma'il narrated to us, he said: Qays narrated to me, from al-Sanabihi al-Ahmasi—Waki' said in his hadith: "al-Sanabihi"—he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am your forerunner at the Hawd (the Cistern), and I will be boasting of your great numbers before the nations, so do not fight one another after me."