فَبِمَا نَقْضِهِم مِّيثَاقَهُمْ وَكُفْرِهِم بَآيَاتِ اللّهِ وَقَتْلِهِمُ الأَنْبِيَاء بِغَيْرِ حَقًّ وَقَوْلِهِمْ قُلُوبُنَا غُلْفٌ بَلْ طَبَعَ اللّهُ عَلَيْهَا بِكُفْرِهِمْ فَلاَ يُؤْمِنُونَ إِلاَّ قَلِيلاً
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سورة النساء
(4/155) This is because of their breaking their covenant and their disbelief in the Verses of Allah and their killing the Prophets wrongfully and their saying: our hearts are covered. Nay! Allah set a seal upon them (their hearts) for their disbelief, so they shall (can) not believe except a few.
Surah An-Nisa