The sealing of hearts (khatm)

كَذَٰلِكَ حَقَّتْ كَلِمَتُ رَبِّكَ عَلَى ٱلَّذِينَ فَسَقُوٓا۟ أَنَّهُمْ لَا يُؤْمِنُونَ

Thus the word [i.e., decree] of your Lord has come into effect upon those who defiantly disobeyed - that they will not believe.