Musnad Ahmad 30:2671

Yazid narrated to us, he said: Muhammad narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurairah, and Muhammad, from the one who heard Abu Salih al-Samman narrating from Abu Hurairah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you fights, let him avoid the face."