Sahih al-Bukhari 1294
صحيح البخاري#1294SahihNarrated `Abdullah:the Prophet (ﷺ) said, "He who slaps his cheeks, tears his clothes and follows the ways and traditions of the Days of Ignorance is not one of us
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: 23:52