It is narrated from Hazrat Anas (may Allah be pleased with him) that once during the Prophethood, a Bedouin came and urinated in the Prophet's Mosque. The Prophet (peace and blessings be upon him) said, "Leave him," and ordered that a bucket of water be poured over it.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 12709