كتاب الطهارة
2  
The Book of Purification
(4)
Chapter: The virtue of performing wudu’ and salat
(4)
باب فَضْلِ الْوُضُوءِ وَالصَّلاَةِ عَقِبَهُ ‏‏
Sahih Muslim 232a

Humran, the freed slave of Uthman reported:

One day Uthman b. Affan performed the ablution well, and then said: I saw Allah's Messenger (ﷺ) perform ablution, the best ablution, and then observed: He who performed ablution like this and then went towards the mosque and nothing (but the love of) prayer urged him (to do so), all his previous (minor) sins would be expiated.
حَدَّثَنَا هَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، حَدَّثَنَا ابْنُ وَهْبٍ، قَالَ وَأَخْبَرَنِي مَخْرَمَةُ بْنُ بُكَيْرٍ، عَنْ أَبِيهِ، عَنْ حُمْرَانَ، مَوْلَى عُثْمَانَ قَالَ تَوَضَّأَ عُثْمَانُ بْنُ عَفَّانَ يَوْمًا وُضُوءًا حَسَنًا ثُمَّ قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ ثُمَّ قَالَ ‏ "‏ مَنْ تَوَضَّأَ هَكَذَا ثُمَّ خَرَجَ إِلَى الْمَسْجِدِ لاَ يَنْهَزُهُ إِلاَّ الصَّلاَةُ غُفِرَ لَهُ مَا خَلاَ مِنْ ذَنْبِهِ ‏"‏ ‏.‏
Reference : Sahih Muslim 232a
In-book reference : Book 2, Hadith 15
USC-MSA web (English) reference : Book 2, Hadith 446
  (deprecated numbering scheme)