Sahih Muslim 1546
صحيح مسلم#1546SahihMuhammad reported:I asked Anas whether the Messenger of Allah (ﷺ) observed Qunut in the dawn prayer. He said: Yes, (he did so) after the ruku', for a short while
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 5:379