Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

that his father said: "We were with the Messenger of Allah (saw) when some of the people said: 'Why do you not stop with us to rest a while, O Messenger of Allah?' He said: 'I am afraid that you will sleep and miss the prayer.' Bilal said: 'I will wake you up.' So they lay down and slept, and Bilal leaned back on his mount. Then the Messenger of Allah (saw) woke up when the sun had already started to rise, and he said: 'O Bilal, what about what you told us?' He said: 'I have never slept like that before.' The Messenger of Allah (saw) said: 'Allah, the Mighty and Sublime, takes your souls when He wills and sends them back when He wills. Stand up O Bilal and call the people to prayer.' Then Bilal stood up and called the Adhan, and they performed Wudhu'" - that is, when the sun had risen (fully) - "then he stood and lead them in prayer." (Sahih)