Sahih Muslim 915
صحيح مسلم#915SahihAbu Huraira reported:The Messenger of Allah (ﷺ) said: SayAmin when the Imam says Amin, for it anyone's utterance of Amin synchronises with that of the angels, he will be forgiven his past sins
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: 4:77