Sahih Muslim 833
صحيح مسلم#833SahihAnas reported:(The people) stood up for prayer and the Messenger of Allah (ﷺ) was whispering to a man, and in the narration of 'Abd al-Warith (the words are): The Apostle of Allah (ﷺ) was having a private conversation with a man, and did not start the prayer till the people dozed off
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: 3:154