Jami` at-Tirmidhi 453
جامع الترمذي#453Da'ifAli said:"Al-Witr is not incumbent like your obligatory prayers, but it is a Sunnah of Allah's Messenger who said: "Indeed Allah is Witr (One), and He loves Al-Witr, so perform Al-Witr O people of the Qur'an
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan
Zubair Ali ZaiDaif
In-book reference: 3:2