Surah An-Nisa, Verse 49

أَلَمۡ تَرَ إِلَى ٱلَّذِينَ يُزَكُّونَ أَنفُسَهُمۚ بَلِ ٱللَّهُ يُزَكِّي مَن يَشَآءُ وَلَا يُظۡلَمُونَ فَتِيلًا٤٩

alam tara ilā alladhīna yuzakkūna anfusahum bali l-lahu yuzakkī man yashāu walā yuẓ'lamūna fatīlan

Have you not seen those who claim themselves to be pure? Rather, Allāh purifies whom He wills, and injustice is not done to them, [even] as much as a thread [inside a date seed].