Sahih Muslim 1020
صحيح مسلم#1020SahihAbu Sa'id al-Khudri reported:The noon prayer would start and one would go to al-Baqi' and after having relieved himself he would perform ablution and then come, while the Messenger of Allah (ﷺ) would be in the first rak'ah, because he would prolong it so much
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: 4:182