Surah Fussilat, Verse 5:
وَقَالُوا قُلُوبُنَا فِي أَكِنَّةٍ مِّمَّا تَدْعُونَا إِلَيْهِ وَفِي آذَانِنَا وَقْرٌ وَمِن بَيْنِنَا وَبَيْنِكَ حِجَابٌ فَاعْمَلْ إِنَّنَا عَامِلُونَ
And they say: Our hearts are under coverings from that to which you call us, and there is a heaviness in our ears, and a veil hangs between us and you, so work, we too are working.