Sunan an-Nasa'i 1700
سنن النسائي#1700SahihIt was narrated that Ubayy bin Ka'b said:"In the first rak'ah of witr, the Messenger of Allah (ﷺ) used to recite: "GLorify the Name of your Lord, the Most High;" in the second; "Say: O you disbelievers!" and in the third; "Say: He is Allah, (the) One
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: 20:103