Allah, the Exalted, says:

"Verily, As-Salat (the prayer) prevents from Al-Fahsha' (i.e., great sins of every kind, unlawful sexual intercourse) and Al-Munkar (i.e., disbelief, polytheism, and every kind of evil, wicked deed).'' (29:45)

1042. Abu Hurairahu (May Allah be pleased with him) reported: I heard the Messenger of Allah (PBUH) saying, "Say, if there were a river at the door of one of you in which he takes a bath five times a day, would any soiling remain on him?'' They replied, "No soiling would left on him.'' He (PBUH) said, '' That is the five (obligatory) Salat (prayers). Allah obliterates all sins as a result of performing them.''
[Al-Bukhari and Muslim].

Commentary:  This Hadith tells us about the merit and benefits of the performance of the prescribed five daily Salat, performing them will wash off one's sins, but this is true of only such Salat which is performed in accordance with Sunnah, i.e., punctually in exactly the manner showed by the Prophet (PBUH), and not of that which is offered at will in one's own way.

1043. Jabiru (May Allah be pleased with him) reported: The Messenger of Allah (PBUH) said, "The similitude of the five (obligatory) Salat  is like a river running at the door of one of you in which he takes a bath five times a day.''
[Muslim].

1044. Ibn Mas`ud (May Allah be pleased with him) reported: A man kissed a woman. So he came to the Messenger of Allah (PBUH) and informed him about it. Then Allah revealed this Ayah: "And perform the Salat, between the two ends of the day and in some hours of the night. Verily, the good deeds efface the evil deeds (i.e., minor sins).'' (11:114) The man asked the Messenger of Allah (PBUH) whether this applies to him only. The Messenger of Allah (PBUH) said, "It applies to all of my Ummah.''
[Al-Bukhari and Muslim].

Commentary:  "Between the ends of the day'' means Fajr and Maghrib prayers. Some people think it refers to `Isha' prayer while some think it means the Maghrib and `Isha' prayers. "In some hours of the night'' means the Tahajjud prayers. This Ayah of the Qur'an has been quoted here to stress that Salat is an act of great virtue and an expiation of sins, but only for minor sins because the major sins will not be pardoned without sincere repentance.

1045. Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (PBUH) said, "The five (daily) Salat (prayers) and the Friday (prayer) to the Friday (prayer) expiate whatever (minor sins) may be committed in between, so long as major sins are avoided.''
[Muslim].

Commentary:  This Hadith elucidates that the minor sins committed during the interval of the five prescribed Salat and in the period intervening between one Jumu`ah and the other are pardoned with the performance of the five-time prescribed Salat and the Jumu`ah prayer, provided one does not commit major sins which are not forgiven without repentance. Sins like Shirk (associating someone with Allah in worship), disobedience of parents, false oath, false evidence, encroachment on an orphan's property, calumny against chaste women, etc., fall in the category of major sins and will not be forgiven by means of Salat only.

1046. `Uthman bin `Affan (May Allah be pleased with him) reported: I heard Messenger of Allah (PBUH) saying, "When the time for a prescribed Salat is due and a Muslim performs its Wudu' and its acts of bowing and prostration properly, this Salat will be an expiation for his past sins, so long as he does not commit major sins, and this applies for ever.''
[Muslim].

Commentary:  This Hadith stresses the importance of performing Salat with all its essential prerequisites, i.e., Wudu' and concentration of mind. Such a Salat will expiate the sins.