Sunan at-Tirmidhi (Jami-al-Tirmidhi), Chapter: Taharah (Purification)

narrated that a villager came to the mosque; the Allah's Messenger (SAW) was also sitting there. He offered Salah and prayed: "0 Allah have mercy on me and on Muhammad and do not have mercy on anyone else besides us." The Prophet (SAW) turned towards him and said, "You have limited the application of a very large thing (Mercy)." There had not passed enough time when this man passed urine in the mosque. The people towards him, but the Prophet (SAW) said. "Pour a bucket of water over it." He also said, "Indeed, you are sent only as those who make things easy and not as those who create difficulties." [Ahmed7804, Bukhari 220, Nisai 1216, Abu Dawud 380]