Sahih Bukhari
Good Manners and Form (Al-Adab)
Volume: 008 / Book Number: 073 / Hadith Number: 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.