Sahih al-Bukhari 6288
صحيح البخاري#6288SahihNarrated `Abdullah:the Prophet (ﷺ) said "When three persons are together, then no two of them should hold secret counsel excluding the third person
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 79:60