Sahih Muslim 1231
صحيح مسلم#1231SahihAnas b. Malik reported:The Messenger of Allah (ﷺ) said: Spitting in a mosque is a sin, and its expiation is that it should be buried
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: 5:69