Quran 63:3 — Surah Al-Munafiqun, ayah 3

ذَٰلِكَ بِأَنَّهُمۡ ءَامَنُواْ ثُمَّ كَفَرُواْ فَطُبِعَ عَلَىٰ قُلُوبِهِمۡ فَهُمۡ لَا يَفۡقَهُونَ

That is because they believed, and then they disbelieved; so their hearts were sealed over, and they do not understand

To je zato što su vjernici bili, pa nevjernici postali, i onda su im srca zapečaćena, pa ne shvaćaju.