It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "What do you think: if a river flowed past someone's door and he bathed in it five times every day, would any dirt remain on his body?" (I think he (peace and blessings be upon him) said this.) They replied: No dirt of his would remain. He (peace and blessings be upon him) said: "Such are the five prayers, through which evil deeds are removed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4971