Sunan Abi Dawud 1422
سنن أبي داود#1422SahihNarrated AbuAyyub al-Ansari: The Prophet (ﷺ) said: The witr is a duty for every Muslim so if anyone wishes to observe it with five rak'ahs, he may do so; if anyone wishes to observe it with three, he may do so, and if anyone wishes to observe it with one, he may do so
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 8:7