Abu Dawud
Prayer
Book Number: 002 / Hadith Number: 1429
Narated By Abu Qatadah : The Prophet (pbuh) asked Abu Bakr: When do you observe the witr?
He replied: I observe the witr prayer in the early hours of the night.
The Prophet (pbuh) asked Umar: When do you observe the witr?
He replied: At the end of the night.
He then said to AbuBakr: This has followed it with care; and he said to Umar: He has followed it with strength.