Musnad Ahmad 400
It was narrated from Hisham bin `Urwah:
My father told me that Humran told him: `Uthman (رضي الله عنه) did wudoo’ in al-Balat (a paved area in Madinah) then he said, i shall tell you a hadeeth that I heard from the Messenger of Allah (ﷺ) . Were it not for a verse in the Book of Allah, I would not have told you it. I heard the Prophet (ﷺ) say: `Whoever does wudoo’ and does it well, then goes in and prays, his sins between that prayer and the next will be forgiven, until he prays [the second prayer].”
حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، أَخْبَرَنِي أَبِي أَنَّ حُمْرَانَ، أَخْبَرَهُ قَالَ تَوَضَّأَ عُثْمَانُ رَضِيَ اللَّهُ عَنْهُ عَلَى الْبَلَاطِ ثُمَّ قَالَ لَأُحَدِّثَنَّكُمْ حَدِيثًا سَمِعْتُهُ مِنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَوْلَا آيَةٌ فِي كِتَابِ اللَّهِ مَا حَدَّثْتُكُمُوهُ سَمِعْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ مَنْ تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ ثُمَّ دَخَلَ فَصَلَّى غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الصَّلَاةِ الْأُخْرَى حَتَّى يُصَلِّيَهَا‏.‏