Narrated from Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When a dog drinks water or anything else from someone's vessel, he should wash it seven times."

Narrated Abdullah bin Umar (may Allah be pleased with them): During the time of Allah's Messenger (peace be upon him), dogs used to come and go in the mosque, and sometimes they would urinate there, but the people did not sprinkle water or anything (to clean) because of their coming and going.