Sahih al-Bukhari 260
صحيح البخاري#260SahihNarrated Maimuna:The Prophet (ﷺ) took the bath of Janaba. (sexual relation or wet dream). He first cleaned his private parts with his hand, and then rubbed it (that hand) on the wall (earth) and washed it. Then he performed ablution like that for the prayer, and after the bath he washed his feet
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: 5:13