Sahih Muslim 231a
Humran b. Aban reported:
I used to fetch water for 'Uthman for his purification. Never was there a day that he did not take a bath with a small quantity of water. And Uthman said: The Messenger of Allah (ﷺ) at the time of our returning from our prayer told us (certain things pertaining to purification). Mis'ar said: I find that it was afternoon prayer. He said: I do not know whether I should tell you a thing or keep quiet. We said: Messenger of Allah, tell us if it is good and if it is otherwise, Allah and His Apostle know better. Upon this he said: A Muslim who purifies (himself) and completes purification as enjoined upon him by Allah and then offers the prayers, that will be expiation (of his sins he committed) between these (prayers).
حَدَّثَنَا أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ جَمِيعًا عَنْ وَكِيعٍ، قَالَ أَبُو كُرَيْبٍ حَدَّثَنَا وَكِيعٌ، عَنْ مِسْعَرٍ، عَنْ جَامِعِ بْنِ شَدَّادٍ أَبِي صَخْرَةَ، قَالَ سَمِعْتُ حُمْرَانَ بْنَ أَبَانَ، قَالَ كُنْتُ أَضَعُ لِعُثْمَانَ طَهُورَهُ فَمَا أَتَى عَلَيْهِ يَوْمٌ إِلاَّ وَهُوَ يُفِيضُ عَلَيْهِ نُطْفَةً ‏.‏ وَقَالَ عُثْمَانُ حَدَّثَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم عِنْدَ انْصِرَافِنَا مِنْ صَلاَتِنَا هَذِهِ - قَالَ مِسْعَرٌ أُرَاهَا الْعَصْرَ - فَقَالَ ‏"‏ مَا أَدْرِي أُحَدِّثُكُمْ بِشَىْءٍ أَوْ أَسْكُتُ ‏"‏ ‏.‏ فَقُلْنَا يَا رَسُولَ اللَّهِ إِنْ كَانَ خَيْرًا فَحَدِّثْنَا وَإِنْ كَانَ غَيْرَ ذَلِكَ فَاللَّهُ وَرَسُولُهُ أَعْلَمُ ‏.‏ قَالَ ‏"‏ مَا مِنْ مُسْلِمٍ يَتَطَهَّرُ فَيُتِمُّ الطُّهُورَ الَّذِي كَتَبَ اللَّهُ عَلَيْهِ فَيُصَلِّي هَذِهِ الصَّلَوَاتِ الْخَمْسَ إِلاَّ كَانَتْ كَفَّارَاتٍ لِمَا بَيْنَهَا ‏"‏ ‏.‏