Ibn Umar (may Allah be pleased with them both) said that Umar bin al-Khattab (may Allah be pleased with him) used to say in a loud voice in the mosque: "Avoid idle talk in the mosque." Ibn Umar (may Allah be pleased with them both) said: I used to spend the night in the mosque in the time of the Prophet (peace and blessings be upon him), and I was an unmarried young man. Dogs would come and go in the mosque and urinate, yet the people did not even sprinkle water over it.
(b) Abu Bakr al-Isma'ili (may Allah have mercy on him) said: The mosque was not closed in those days. It is possible that they urinated, and that the Prophet (peace and blessings be upon him), the noble Companions (may Allah be pleased with them) and the narrator did not know the place. The command that the Prophet (peace and blessings be upon him) gave regarding the Bedouin's urine also falls under the same ruling of impurity.
(c) Maymunah (may Allah be pleased with her) said: Concerning a puppy, the Prophet (peace and blessings be upon him) gave a command and it was taken out; then he (peace and blessings be upon him) took water and sprinkled it over that place.
(d) Abu Hurayrah (may Allah be pleased with him) said that, because a dog put its mouth into a vessel, the command was given to wash it a number of times and to pour that water away. All of these things indicate that it is impure.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4244