Musnad Ahmad 761:1

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, the son of the brother of Abu Ruhm informed me that he heard Abu Ruhm al-Ghifari—and he was one of the companions of the Prophet, may God bless him and grant him peace, who pledged allegiance under the tree—saying: I went out on an expedition with the Prophet, may God bless him and grant him peace, the expedition of Tabuk. When he departed, he traveled by night, and I traveled near him. Drowsiness overcame me, and I began to wake up while my mount had drawn near to his mount. Its proximity would startle me for fear that I might strike his foot in the stirrup, so I would pull my mount back until my eyes overcame me in the middle of the night. My mount rode against his mount, and the foot of the Prophet, may God bless him and grant him peace, was in the stirrup, and it struck his foot. I did not wake up except at his saying: "Hass" (an exclamation of pain). I raised my head and said: "Seek forgiveness for me, O Messenger of God." He said: "Ask." He began asking me about those who stayed behind from the Banu Ghifar, and I informed him. Then he asked me: "What did the tall, red-complexioned, curly-haired—or he said: short—men do?" 'Abd al-Razzaq is in doubt. "Those who have livestock at Shaziyat Sharkh?" He said: I mentioned them among the Banu Ghifar, but I did not recall them until I mentioned a group from Aslam. I said: "O Messenger of God, those are a group from Aslam, and they have stayed behind." The Messenger of God, may God bless him and grant him peace, said: "What prevents one of those, when he stays behind, from carrying an energetic man in the way of God upon one of his camels? For the most beloved of my people to me is that the Emigrants from Quraysh, the Helpers (Ansar), Ghifar, and Aslam should not stay behind from me."