due time, and completes its Ruku and Sujood with humility, then it is upon the mercy of Allah Almighty to forgive him. And the one who does not offer them [the 5 daily Salahs], then he will be deprived of the mercy of Allah Almighty. If He Almighty wills, He may forgive him and if He wills, He may punish him. (Abu Dawood, Raqm 1, 425/186)

Salah wipes off sins

O devotees of Rasool! Those fortunate Muslims who offer the five daily Salahs, all their sins are forgiven. The Holy Rasool صَلَّى اللّٰهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم has stated: ‘If anyone among you has a stream in his courtyard and takes bath in it 5 times a day, would any dirt remain on him?’ People humbly replied: ‘No.’ The Holy Rasool صَلَّى اللّٰهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم said: ‘Salah wipes away sins in the same manner as water washes away dirt.’ (Ibn-e-Majah, vol. 2, pp. 165, Hadees 1397)  

Every Salah is an atonement for the previous sins

Those fortunate individuals who are used to offering Salah, let’s suppose, if sins get committed by them in between two Salahs, then the second Salah becomes an atonement for those sins. I.e. Allah Almighty forgives the sins committed between two Salahs. 

Sayyiduna Haaris رَضِىَ اللهُ تَعَالٰی عَـنْهُ narrates that one day, we and Sayyiduna Usman-e-Ghani رَضِىَ اللهُ تَعَالٰی عَـنْهُ were seated. In the meanwhile, the Muazzin (one who calls Azan) came. Sayyiduna Usman-e-Ghani رَضِىَ اللهُ تَعَالٰی عَـنْهُ asked for water and performed Wudhu. Then, he رَضِىَ اللهُ تَعَالٰی عَـنْهُ said: ‘I saw the Holy Rasool صَلَّى اللّٰهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم performing Wudhu in the similar manner. I also heard the Holy Rasool صَلَّى اللّٰهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم saying: ‘The one who performs Wudhu the way I have performed and then offers the Zuhr Salah, Allah Almighty forgives his sins, i.e. the sins that were committed between Fajr and Zuhr. Then when he offers ‘Asr Salah, then Allah Almighty forgives his sins committed between Zuhr and ‘Asr. Then when he offers Maghrib Salah, then Allah Almighty forgives his sins committed between ‘Asr and Maghrib. Then when he offers Isha Salah, then Allah Almighty forgives his sins committed between Maghrib and Isha. Then it is possible that he spends the entire night lying down. Then when he gets up, performs Wudu and offers Fajr Salah, then the sins committed between ‘Isha and Fajr are forgiven. These are the virtuous deeds that remove the evils.’           (Al Ahadees-ul-Mukhtarah, vol. 1, pp. 450, Hadees 324)