Good Manners and Form (Al-Adab)

Bukhari :: Book 8 :: Volume 73 :: Hadith 54

Narrated Anas bin Malik:

A bedouin urinated in the mosque and the people ran to (beat) him. Allah's Apostle said, "Do not interrupt his urination (i.e. let him finish)." Then the Prophet asked for a tumbler of water and poured the water over the place of urine.