وَجَعَلنا عَلىٰ قُلوبِهِم أَكِنَّةً أَن يَفقَهوهُ وَفي آذانِهِم وَقرًا ۚ وَإِذا ذَكَرتَ رَبَّكَ فِي القُرآنِ وَحدَهُ وَلَّوا عَلىٰ أَدبارِهِم نُفورًا

And We have placed over their hearts coverings, lest they understand it, and in their ears deafness. And when you mention your Lord alone in the Qur'an, they turn back in aversion.