Sahih Al Bukhari Hadith Number 996

Narrated `Aisha: Allah’s Messenger (peace be upon him) offered witr prayer at different nights at various hours extending (from the `Isha’ prayer) up to the last hour of the night.

14  Witr Prayer
Hadith number 996
Volume no 2
Chapter: 2 (The timing of the Salat-ul-Witr (Witr prayer)