Sahih Bukhari
Ablutions (Wudu)
Volume: 001 / Book Number: 004 / Hadith Number: 219
Narrated Abu Huraira:
A Bedouin stood up and started making water in the mosque. The people caught him but the Prophet ordered them to leave him and to pour a bucket or a tumbler of water over the place where he had passed the urine. The Prophet then said, "You have been sent to make things easy and not to make them difficult."