Abu Dawud Book 2, Hadith Number 1312.
Chapter : The time when the prophet peacebeuponhim used to get up at night for prayer.
Narated By Masruq : I asked ‘Aisha about the prayer of the Apostle of Allah (PBUH), and I said to her: At what time he prayed at night? She replied: When he heard the cock croe, he got up and prayed.