Abu Dawud Book 2, Hadith Number 1413.
Chapter : To observe the witr is commendable.
Narated By Kharijah ibn Hudhafah al-Adawi : The Apostle of Allah (PBUH) came out to us and said: Allah the Exalted has given you an extra prayer which is better for you then the red camels (i.e. high breed camels). This is the witr which Allah has appointed for you between the night prayer and the daybreak.