Musannaf Ibn Abi Shayba 36:328

Ghundar narrated to us, from Shu'bah, from Jami' ibn Shaddad, who said: I heard 'Abd al-Rahman ibn Abi 'Alqamah, who said: I heard 'Abdullah ibn Mas'ud, who said: We were returning with the Messenger of Allah (may Allah bless him and grant him peace) from al-Hudaybiyah. They mentioned that they camped on *dahas* of the earth—meaning by *dahas*, sand. He said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Who will keep watch for us?" Bilal said: "I will." He said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Then we shall sleep." So they slept until the sun rose. People woke up, among them were so-and-so and so-and-so, and among them was 'Umar. He said: We said: "Speak loudly" (meaning: talk). He said: The Prophet (may Allah bless him and grant him peace) woke up and said: "Do as you were doing." They said: We did so. He said: "Do likewise for whoever sleeps or forgets." He said: The she-camel of the Messenger of Allah (may Allah bless him and grant him peace) went astray, so I searched for it. He said: I found its rope caught on a tree, so I came to the Messenger of Allah (may Allah bless him and grant him peace), and he mounted it, and we traveled. He said: When the revelation would descend upon the Prophet (may Allah bless him and grant him peace), it would be intense, and we would recognize that in him. He said: So he moved away, distancing himself behind us. He said: He began to cover his head with his garment, and it became intense for him until we knew that it had been revealed to him. They came to us and informed us that it had been revealed to him: "Indeed, We have given you a clear conquest."