He replied: I observe the witr prayer in the early hours of the night.
The Prophet (ﷺ) asked Umar: When do you observe the witr?
He replied: At the end of the night.
He then said to Abu Bakr: This has followed it with care; and he said to Umar: He has followed it with strength.
In-book : Book 8, Hadith 19
English translation : Book 8, Hadith 1429