Surah Al-Munafiqun, Verse 3

ذَٰلِكَ بِأَنَّهُمۡ ءَامَنُواْ ثُمَّ كَفَرُواْ فَطُبِعَ عَلَىٰ قُلُوبِهِمۡ فَهُمۡ لَا يَفۡقَهُونَ٣

dhālika bi-annahum āmanū thumma kafarū faṭubiʿa ʿalā qulūbihim fahum lā yafqahūna

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