Sahih al-Bukhari 888
صحيح البخاري#888SahihNarrated Anas:Allah's Messenger (ﷺ) said, "I have told you repeatedly to use the Siwak. (The Prophet (ﷺ) put emphasis on the use of the Siwak
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: 11:13