It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings be upon him) say: "Tell me, if there were a river at the door of one of you and he bathed in it five times every day, would any of his dirt remain?" They said: Not a trace of his dirt would remain. He (peace and blessings be upon him) said: "That is the likeness of the five prayers; through them Allah Almighty wipes out sins."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1693