Sahih Muslim 1547
صحيح مسلم#1547SahihAnas b. Malik reported:The Messenger of Allah (ﷺ) observed Qunut for a month in the dawn prayer after ruku' and invoked curse upon Ri'l, Dhakwan, and said that 'Usayya had disobeyed Allah and His Apostle (ﷺ)
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: 5:380