Sahih Bukhari Volume 1, Book 4, Hadith 160

وَعَنْ إِبْرَاهِيمَ، قَالَ قَالَ صَالِحُ بْنُ كَيْسَانَ قَالَ ابْنُ شِهَابٍ وَلَكِنْ عُرْوَةُ يُحَدِّثُ عَنْ حُمْرَانَ،، فَلَمَّا تَوَضَّأَ عُثْمَانُ قَالَ أَلاَ أُحَدِّثُكُمْ حَدِيثًا لَوْلاَ آيَةٌ مَا حَدَّثْتُكُمُوهُ، سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏"‏ لاَ يَتَوَضَّأُ رَجُلٌ فَيُحْسِنُ وُضُوءَهُ، وَيُصَلِّي الصَّلاَةَ إِلاَّ غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الصَّلاَةِ حَتَّى يُصَلِّيَهَا ‏"‏‏.‏ قَالَ عُرْوَةُ الآيَةُ ‏{‏إِنَّ الَّذِينَ يَكْتُمُونَ مَا أَنْزَلْنَا مِنَ الْبَيِّنَاتِ‏}

Narrated Humran: When Uthman performed the ablution ,he said,"I am going to tell you a Hadith which I would not have told you except for( had I not been compelled by) a certain Holy verse.I heard the prophet(saw) saying "If a man performs ablution perfectly and when offers the compulsory (congregational) salat,Allah will forgive his sins comitted between that(prayer) and the (next) prayer till he offer it." The subnarrator Urwah said: This verse is:" Verily, those who conceal the clear proofs and evidences and the guidance which we have sent down ...."[v.2:159]