(33) باب إِذَا شَرِبَ الْكَلْبُ فِي إِنَاءِ أَحَدِكُمْ فَلْيَغْسِلْهُ سَبْعًا
And 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.)"
Reference: Sahih al-Bukhari 174
In-book reference: Book 4, Hadith 40
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 4, Hadith 174