Volume 2, Book 16, Number 108:
Allah's Apostle used to pray eleven Rakat at night and that was his night prayer and each of his prostrations lasted for a period enough for one of you to recite fifty verses before Allah's Apostle raised his head. He also used to pray two Rakat (Sunna) before the (compulsory) Fajr prayer and then lie down on his right side till the Muadh-dhin came to him for the prayer.
Allah's Apostle offered Witr prayer at different nights at various hours extending (from the 'Isha' prayer) up to the last hour of the night.
Narrated 'Aisha :
The Prophet (p.b.u.h) used to offer his night prayer while I was sleeping across in his bed. Whenever he intended to offer the Witr prayer, he used to wake me up and I would offer the Witr prayer too.