Surah Al-Munafiqoon Verse 3 - English Translation by Ali Unal
Surah Al-Munafiqoonذَٰلِكَ بِأَنَّهُمۡ ءَامَنُواْ ثُمَّ كَفَرُواْ فَطُبِعَ عَلَىٰ قُلُوبِهِمۡ فَهُمۡ لَا يَفۡقَهُونَ
That is because they declared faith but thereafter (inwardly) disbelieved, so a seal has been set on their hearts so that they do not grasp the truth (and cannot recover the ability to reach to it)