Sunan an-Nasa'i 1676
سنن النسائي#1676SahihIt was narrated that Ali, may Allah (SWT) be pleased with him, said:"Witr is not essential like the obligatory prayers, but it is the sunnah of the Messenger of Allah (ﷺ)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 20:79