Ablutions (Wudu')

Bukhari :: Book 1 :: Volume 4 :: Hadith 176

Narrated Abu Huraira:

Allah's Apostle said, "A person is considered in prayer as long as he is waiting for the prayer in the mosque as long as he does not do Hadath." A non-Arab man asked, "O Abii Huraira! What is Hadath?" I replied, "It is the passing of wind (from the anus) (that is one of the types of Hadath)."