The End of the Time for Witr
Question :
What is the latest time Witr may be performed?
Answer:
It is at the end of the night, before Fajr prayer begins, according to the words of the Prophet:
The night prayer and the day prayer are two by two... so if any of you fears that the morning is nigh, he should pray one Rak'ah, which will be Witr for what he has already prayed.
Source:
Ibn Baz
Fatawa Islamiyah, Vol. 2 Page 305