Sahih al-Bukhari 172
صحيح البخاري#172SahihNarrated Abu Huraira:Allah's Messenger (ﷺ) said, "If a dog drinks from the utensil of anyone of you it is essential to wash it seven times
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: 4:38