Sahih Bukhari Volume 1, Book 10, Hadith Number 506

Narated By Abu Huraira : I heard Allah’s Apostle saying, “If there was a river at the door of anyone of you and he took a bath in it five times a day would you notice any dirt on him?” They said, “Not a trace of dirt would be left.” The Prophet added, “That is the example of the five prayers with which Allah blots out (annuls) evil deeds.”