Abu Dawud Book 2, Hadith Number 1316.
Chapter : The time when the prophet peacebeuponhim used to get up at night for prayer.
Narated By Anas b. Malik : Anas said (explaining the meaning) of the following Qur’anic verse “Who forsake their beds to cry unto their Lord in fear and hope, and spend of what We have bestowed on them” (xxxii. 6): The people used to remain awake between the sunset and the night prayers and would pray. Al-Hasan used to say: (This verse means) the prayer and vigil at night.