Sahih al-Bukhari 5822
صحيح البخاري#5822SahihNarrated Abu Sa`id Al-Khudri:The Prophet (ﷺ) forbade Ishtimal-as-Samma' and that a man should sit in an Ihtiba' posture in one garment, nothing of which covers his private parts
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: 77:39