"abu muslim narrates: i went to see abu umaamah (may allah be pleased with him) while he was in the masjid. i asked him if he had really heard the holy prophet (pbuh) saying, "when a person performs wudhu with right performance and then says his fardh salaat, allah forgives him all the sins committed that day by his feet in going towards evil, by his hands in doing evil, by his ears in listening to evil, by his eyes in looking at evil and by his heart in thinking of evil.' he replied, 'by allah, i have heard these words from the prophet (pbuh) again and again."
many of the companions have narrated this hadith with slight variations. those endowed with the power of kashf can even witness the sins being shed. it is said of imam abu haneefa (may allah be pleased with him) that he could tell from the water falling down from the limbs of the person performing wudhu as to which sins had been washed off therewith.
in a narration by uthman (may allah be pleased with him), the prophet (pbuh) is reported to have warned against being wrong-headed in committing sins in the hope of getting them redeemed through salaat. we have, really, no ground to behave as such on this account. after all, what is the quality of the salaat that we offer? if allah merely absolves us of our obligation it is his very special favour and grace. again it is the height of ingratitude to disobey allah just because he is clement, merciful and forgiving.