The Messenger of Allah ﷺ said, "Whoever sleeps through the witr prayer or forgets it should pray it as soon as he remembers, or when he wakes up."
حدثنا محمود بن غيلان حدثنا وكيع حدثنا عبد الرحمن بن زيد بن أسلم عن أبيه عن عطاء بن يسار
قال رسول الله ﷺ من نام عن الوتر أو نسيه فليصل إذا ذكر وإذا استيقظ
Sourcing, [sahih]. Abu Dawud also narrated it in Witr, chapter on the supplication after Witr, hadith no. 1431, with a sahih chain from Zayd bin Aslam through the same route. Hakim graded it sahih according to the standard of Bukhari, 1/302, and Dhahabi agreed with him.