Ibn Hibban has:

'Whosoever reaches the dawn, and he did not offer Witr, then there is no Witr for him.'

وَلِابْنِ حِبَّانَ: { مَنْ أَدْرَكَ اَلصُّبْحَ وَلَمْ يُوتِرْ فَلَا وِتْرَ لَهُ } [1]‏ .‏