Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says: In the time of the Prophet (peace and blessings be upon him) I used to spend the night in the mosque, and I was an unmarried young man. In that time dogs would urinate and come and go in the mosque, but the people would not sprinkle (water) over that place.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1153