Musnad Ahmad 985:1

Bahz narrated to us, Hammad ibn Salamah narrated to us, Ya'la ibn 'Ata' informed me, from Abu Hammam—Abu al-Aswad is 'Abdullah ibn Yasar—from Abu 'Abd al-Rahman al-Fihri, who said: I was with the Messenger of Allah, peace and blessings of Allah be upon him, on the expedition of Hunayn. We traveled on a scorching, intensely hot day, and we descended under the shade of trees. When the sun passed its zenith, I put on my armor, mounted my horse, and set off toward the Messenger of Allah, peace and blessings of Allah be upon him, while he was in his tent. I said, "Peace be upon you, O Messenger of Allah, and the mercy of Allah. Is it time to depart?" He said, "Yes." He then said, "O Bilal." He (Bilal) rose from under an acacia tree, as if his shadow were the shadow of a bird, and said, "At your service and ready to obey, and I am your ransom." He said, "Saddle my horse for me." He brought out a saddle whose padding was made of palm fiber, containing neither arrogance nor vanity. He said, "So he saddled it." He said, "He mounted, and we mounted. We lined up against them that evening and throughout the night, and the two cavalries clashed. The Muslims turned, retreating, as Allah the Almighty said. The Messenger of Allah, peace and blessings of Allah be upon him, said, 'O servants of Allah, I am the servant of Allah and His Messenger.' Then he said, 'O company of the Emigrants, I am the servant of Allah and His Messenger.'" He said, "Then the Messenger of Allah, peace and blessings of Allah be upon him, dismounted from his horse, took a handful of dust, and the one who was closer to him than I informed me that he struck their faces with it and said, 'May the faces be disfigured.' So Allah the Almighty defeated them." Ya'la ibn 'Ata' said: Their sons narrated to me from their fathers that they said: "There remained not one of us but that his eyes and mouth were filled with dust, and we heard a clanging between the heaven and the earth like the passing of iron over a copper basin."