Sahih al-Bukhari 174
صحيح البخاري#174SahihAnd narrated Hamza bin 'Abdullah:My father said. "During the lifetime of Allah's Apostle, the dogs used to urinate, and pass through the mosques (come and go), nevertheless they never used to sprinkle water on it (urine of the dog)
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: 4:40