Mishkat al-Masabih
‘Uthman reported God’s messenger as saying, “If anyone performs the ablution well, his sins will come out from his body, even coming out from under his nails.” (Bukhari and Muslim.)
عَنْ عُثْمَانَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنْ تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ خَرَجَتْ خَطَايَاهُ مِنْ جَسَدِهِ حَتَّى تخرج من تَحت أَظْفَاره»
Reference