Surah Al-Isra' (The Night Journey), Verse 46

وَّجَعَلْنَا عَلٰی قُلُوْبِهِمْ اَكِنَّةً اَنْ یَّفْقَهُوْهُ وَفِیْۤ اٰذَانِهِمْ وَقْرًا وَاِذَا ذَكَرْتَ رَبَّكَ فِی الْقُرْاٰنِ وَحْدَهٗ وَلَّوْا عَلٰۤی اَدْبَارِهِمْ نُفُوْرًا ۟

Wa ja'alnaa 'alaa quloo bihim akinnatan any yafqahoohu wa feee aazaanihim waqraa; wa izaa zakarta Rabbaka fil Quraani wahdahoo wallaw 'alaaa adbaarihim nufooraa

“And We put coverings over their hearts (and minds) lest they should understand the Qur'an, and deafness into their ears: when thou dost commemorate thy Lord and Him alone in the Qur'an, they turn on their backs, fleeing (from the Truth).”

Quran 17:46 (Yusuf Ali Translation)