Sahih Muslim 5694
صحيح مسلم#5694SahihIbn Umar reported Allah's Messenger (ﷺ) as saying:When there are three (persons), two should not converse secretly between themselves to the exclusion of the (third) one
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: 39:48