Sahih Muslim 1555
صحيح مسلم#1555SahihAl-Bari' b. 'Azib reported that the Messenger of Allah (ﷺ) observed Qunut in the morning and evening (prayers)
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: 5:388