This verse is: "Verily, those who conceal the clear signs and the guidance which we have sent down...)" (2:159). I heard the Prophet ﷺ saying, 'If a man performs ablution perfectly and then offers the compulsory congregational prayer, Allah will forgive his sins committed between that (prayer) and the (next) prayer till he offers it.  

أَلاَ أُحَدِّثُكُمْ حَدِيثًا لَوْلاَ آيَةٌ مَا حَدَّثْتُكُمُوهُ سَمِعْتُ النَّبِيَّ ﷺ 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}  

I heard from 'Uthman b. 'Affan and he was in the courtyard of the mosque, when the Mu'adhdhin (announcer of the prayer) came to him at the time of afternoon prayer. So the ('Uthman) called for the ablution water and performed ablution and then said: By Allah, I am narrating to you a hadith. If there were not a verse in the Book of Allah, I would have never narrated it to you. I heard Messenger of Allah ﷺ say: If a Muslim performs ablution and does it well and offers prayer, all his (sins) daring the period from one prayer to another would be pardoned by Allah.  

سَمِعْتُ عُثْمَانَ بْنَ عَفَّانَ وَهُوَ بِفِنَاءِ الْمَسْجِدِ فَجَاءَهُ الْمُؤَذِّنُ عِنْدَ الْعَصْرِ فَدَعَا بِوَضُوءٍ فَتَوَضَّأَ ثُمَّ قَالَ وَاللَّهِ لأُحَدِّثَنَّكُمْ حَدِيثًا لَوْلاَ آيَةٌ فِي كِتَابِ اللَّهِ مَا حَدَّثْتُكُمْ إِنِّي سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ لاَ يَتَوَضَّأُ رَجُلٌ مُسْلِمٌ فَيُحْسِنُ الْوُضُوءَ فَيُصَلِّي صَلاَةً إِلاَّ غَفَرَ اللَّهُ لَهُ مَا بَيْنَهُ وَبَيْنَ الصَّلاَةِ الَّتِي تَلِيهَا  

Yahya related to me from Malik from Hisham ibn Urwa from his father from Humran, the mawla of Uthman ibn Affan, that Uthman ibn Affan was once sitting on the Maqaid (the benches surrounding the Madina Mosque, or else a stone near Uthman ibn Affan's house where he sat to discuss with people), when the muadhdhin came and told him that it was time for the asr prayer. He called for water and did wudu. Then he said, "By Allah, I shall tell you something which I would not tell you if it were not in the Book of Allah. I heard the Messenger of Allah ﷺ say, 'If a man does wudu, and makes sure he does it correctly, and then does the prayer, he will be forgiven everything that he does between then and the time when he prays the next prayer.' " Yahya said that Malik said, "I believe he meant this ayat - 'Establish prayer at the two ends of the day and in some watches of the night. Good actions take away wrong actions. That is a reminder for those who remember.' " (Sura 11 ayat 114).  

أَنَّهُ فِي كِتَابِ اللَّهِ مَا حَدَّثْتُكُمُوهُ ثُمَّ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَا مِنِ امْرِئٍ يَتَوَضَّأُ فَيُحْسِنُ وُضُوءَهُ ثُمَّ يُصَلِّي الصَّلاَةَ إِلاَّ غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الصَّلاَةِ الأُخْرَى حَتَّى يُصَلِّيَهَا  

My father told me that Humran told him: ʿUthman ؓ 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: ʿWhoever 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].” (Using translation from Aḥmad 400)   

لَأُحَدِّثَنَّكُمْ حَدِيثًا لَوْلَا آيَةٌ فِي كِتَابِ اللَّهِ لَمَّا حَدَّثْتُكُمُوهُ ثُمَّ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ «مَا مِنِ امْرِئٍ يَتَوَضَّأُ فَيُحْسِنُ الْوُضُوءَ ثُمَّ يُصَلِّي الصَّلَاةَ إِلَّا غُفِرَ لَهُ مَا بَيْنَهُ وَبَيْنَ الصَّلَاةِ الْأُخْرَى حَتَّى يُصَلِّيَهَا»