"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.'"
Sunan an-Nasa'i Book 20, Hadith 114