Jami` at-Tirmidhi 454
جامع الترمذي#454Da'ifSufyan Ath-Thawri and others reported from Abu Ishaq, from Asim bin Damrah, that :Ali said: "Al-Witr is not incumbent like the status of the obligatory prayers, but it is a Sunnah which Allah's Messenger practiced
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Zubair Ali ZaiDaif
In-book reference: 3:3