The Holy Prophet (peace and blessings be upon him) said:
"Let anyone tell me; if a stream flows by the house of any person and he baths in it five times a day, whether any dirt will remain on his body."
The companions replied that no dirt would remain in such a case.
He said, "So is the case with prescribed prayers. Allah forgives men's sins (minor) on their account."
(Bukhari, Muslim)