Sahih Muslim 1511
صحيح مسلم#1511SahihAbu Huraira reported:The Messenger of Allah (ﷺ) said: Anyone amongst you who sat in a place of worship waiting for the prayer is in prayer and his ablution is not broken, the angels invoke blessing upon him (in these words): O Allah! pardon him. O Allah! have mercy upon him
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: 5:344