Musannaf Ibn Abi Shayba 37:293

Yazid ibn Harun narrated to us, from al-Awwam, who said: Mansur ibn al-Mu'tamir narrated to me, from Rib'i, from Hudhayfah, who said: "Draw near, O company of Mudar, for by Allah, you will not cease to persecute and kill every believer until Allah, His angels, and the believers strike you, to the point that you will not be able to defend the bottom of a valley." They said: "Why do you bring us near while we are in this state?" He said: "Indeed, among you is the master of the children of Adam, and indeed, among you are forerunners like the forerunners of horses."