"Abu Hurairah Radhiyallahu anh narrates that once the Prophet Sallallahu alaihi wasallam asked his companions, 'Do you believe that dirt can remain on a person bathing five times a day in a brook running in front of his door?' 'No', replied the companions, 'No dirt can remain on his body.' The Prophet Sallallahu alaihi wasallam remarked: 'So, exactly similar is the effect of salaat offered five times a day. With the Grace of Allah. it washes away all the sins'."
(Sahih Bukhair, Muslim, Ibn Majah, Thirmidhi, Nasaa'i)