﴿ أَلَمْ تَرَ إِلَى ٱلَّذِينَ يُزَكُّونَ أَنفُسَهُم ۚ بَلِ ٱللَّهُ يُزَكِّى مَن يَشَآءُ وَلَا يُظْلَمُونَ فَتِيلًا ﴾

“Art thou not aware of those who consider themselves pure? Nay, but it is God who causes whomever He wills to grow in purity; and none shall be wronged by as much as a hair's breadth.”

Please check ayah 4:52 for complete tafsir.