"Az-Zuhri narrated to me, he said: 'Ata bin Yazid, from Abu Ayyub: The Messenger of Allah ﷺ said: 'Witr is a duty, and whoever wants to pray witr with seven (rak'ahs), let him do so; whoever wants to pray witr with five, let him do so, whoever wants to pray witr with three, let him do so; and whoever wants to pray witr with one, let him do so.'" (Using translation from Nasāʾī 1711)   

قَالَ رَسُولُ اللَّهِ ﷺ «الْوِتْرُ حَقٌّ فَمَنْ شَاءَ أَوْتَرَ بِثَلَاثٍ وَمِنْ شَاءَ أَوْتَرَ بِخَمْسٍ وَمَنْ أَحَبَّ أَنْ يُوتِرَ بِوَاحِدَةٍ فَلْيُوتِرْ بِوَاحِدَةٍ»