Sahih al-Bukhari 291
صحيح البخاري#291SahihNarrated Hisham:as the following Hadith 290. Narrated Abu Huraira: The Prophet (ﷺ) said, "When a man sits in between the four parts of a woman and did the sexual intercourse with her, bath becomes compulsory
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: 5:43