The one who has not prayed the Witr prayer before dawn, then there is no Witr for him
Authentic hadithعن أبي سعيد الخدري رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: «من أدركه الصبح ولم يوتر؛ فلا وتر له».
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: "The one who has not prayed the Witr prayer before dawn, then there is no Witr for him."
Explanation
This narration shows that the time for the Witr prayer expires after daybreak and that this is the normal time range for it. However, if someone wakes up from sleep late, then the time for the Witr is extended for him until the Fajr prayer, as it was reported to have been done by a great number of the Companions (may Allah be pleased with them).
Source · Narrated by Ibn Hebban - Ibn Khuzaymah - Al-Haakim
From the Hadith Encyclopedia (hadeethenc.com).