He who observed the night prayer should make Witr the end of his prayer before dawn. The Messenger of Allah ﷺ used to order them thus. (Using translation from Muslim 751c)
أَنَّ ابْنَ عُمَرَ كَانَ يَقُولُ مَنْ صَلَّى مِنَ اللَّيْلِ فَلْيَجْعَلْ آخِرَ صَلَاتِهِ وِتْرًا قَبْلَ الصُّبْحِ كَذَلِكَ كَانَ رَسُولُ اللهِ ﷺ يَأْمُرُهُمْ