Musannaf Ibn Abi Shayba 36:464

'Affan narrated to us, he said: Hammad bin Salamah narrated to us, he said: Ya'la bin 'Ata' informed us, from Abu Hammam 'Abdullah bin Yasar, from Abu 'Abd al-Rahman al-Fihri, who said: I was with the Messenger of Allah (may Allah bless him and grant him peace) 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 and mounted my horse, and I set off toward the Messenger of Allah (may Allah bless him and grant him peace) while he was in his tent. I said: "Peace be upon you, O Messenger of Allah, and the mercy of Allah. It is time to depart, it is time to depart." He said: "Yes." Then he said: "O Bilal!" And 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." So he brought out a saddle stuffed with palm fiber, in which there was neither arrogance nor vanity. He said: So he saddled it. He said: Then he mounted and we mounted. We stood in ranks against them that evening and that night. Then the two cavalries clashed, and the Muslims turned back, fleeing, as Allah has said. Then the Messenger of Allah (may Allah bless him and grant him peace) 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." Then the Messenger of Allah (may Allah bless him and grant him peace) dismounted from his horse and took a handful of dust. The one who was closer to him than I told me that he struck their faces with it and said: "May the faces be deformed." He said: So Allah defeated them. Ya'la bin 'Ata' said: Their sons narrated to me from their fathers that they said: "There did not remain 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 dragging of iron over a new basin."