Musnad Ahmad 434:1

Abu al-Nadr narrated to us, Hariz narrated to us, from Yazid ibn Sulayh, from Dhu Mikhmar—who was a man from Abyssinia who served the Prophet, may God bless him and grant him peace—who said: We were with him on a journey, and he quickened his pace when he departed, and he used to do that due to the scarcity of provisions. A person said to him: "O Messenger of God, the people have fallen behind you." So he stopped, and the people stopped with him until they had all gathered to him. He said to them: "Would you like for us to take a nap?"—or a person said to him [that]. So he dismounted, and they dismounted. He said: "Who will watch over us tonight?" I said: "I, may God make me a ransom for you." He gave me the halter of his she-camel and said: "Take this; do not be negligent." He said: So I took the halter of the Messenger of God’s she-camel and the halter of my she-camel, and I moved away not far, and I let them go to graze. While I was like that, looking at them, sleep overcame me, and I did not perceive anything until I felt the heat of the sun on my face. I woke up, and I looked to the right and to the left, and there were the two mounts not far from me. I took the halter of the Prophet’s she-camel and the halter of my she-camel, and I came to the nearest of the people and woke him up. I said to him: "Have you prayed?" He said: "No." So the people woke one another up until the Prophet, may God bless him and grant him peace, woke up. He said: "O Bilal, is there water in the vessel?"—meaning the water skin. He said: "Yes, may God make me a ransom for you." He brought him water for ablution, and he performed ablution, not letting any dust touch it. He ordered Bilal, so he gave the call to prayer. Then the Prophet, may God bless him and grant him peace, stood and prayed the two rak'ahs before the morning prayer, not rushing. Then he ordered him, so he performed the iqamah for the prayer, and he prayed, not rushing. A person said to him: "O Prophet of God, we have been negligent." He said: "No. God, the Almighty and Majestic, seized our souls and returned them to us, and we have prayed."