Abu Dawud Book 1, Hadith Number 200.
Chapter : Performing ablution after awaking from sleep.
Narated By Anas : The Companions during the lifetime of the Messenger of Allah (may peace be upon him) used to wait for the night prayer so much so that their heads were lowered down (by dozing). Then they offered prayer and did not perform ablution.
Abu Dawud said: Shubah on the authority of Qatadah added: We lowered down our heads (on account of dozing) in the day of the Messenger of Allah (may peace be upon him).
Abu Dawud said : This tradition has been narrated through a different chain of narrators.