Jami` at-Tirmidhi 460
جامع الترمذي#460Da'ifAli narrated:"Allah's Messenger would perform Al-Witr with three, reciting nine Surah from the Mufassal in them, reciting three Surah in each Rak'ah with Say: "Allah is One." At the end of them."Muhammad bin Sirin said: "They would perform Al-Witr with five, with three, and with one Rak'ah, and they considered all of that to be good
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirVery Daif
Al-AlbaniVery Daif
Zubair Ali ZaiDaif
In-book reference: 3:8