Make haste to perform the Witr prayer before the morning
Authentic hadithعن ابن عمر رضي الله عنهما أن النبي صلى الله عليه وسلم قال: «بادروا الصبح بالوتر».
Ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Make haste to perform the Witr prayer before the morning."
Explanation
The Hadīth indicates the recommendation to delay the Witr prayer until the last part of the night. However, the one who delays his Witr prayer to the last part of the night should be cautious to perform it before dawn. The time for voluntary night prayer ends with the break of dawn, so, if dawn broke before he prays Witr, then he misses the virtue of this prayer.
Source · Narrated by Muslim
From the Hadith Encyclopedia (hadeethenc.com).