Sahih Bukhari Volume 001, Book 010, Hadith Number 569.
Narated By 'Abdullah bin Abi Qatada : My father said, "One night we were traveling with the Prophet and some people said, 'We wish that Allah's Apostle would take a rest along with us during the last hours of the night.' He said, 'I am afraid that you will sleep and miss the (Fajr) prayer.' Bilal said, 'I will make you get up.' So all slept and Bilal rested his back against his Rahila and he too was overwhelmed (by sleep) and slept. The Prophet got up when the edge of the sun had risen and said, 'O Bilal! What about your statement?' He replied, 'I have never slept such a sleep.' The Prophet said, 'Allah captured your souls when He wished, and released them when He wished. O Bilal! Get up and pronounce the Adhan for the prayer.' The Prophet performed ablution and when the sun came up and became bright, he stood up and prayed."