Hardening of the heart (qaswat al-qalb)

فِى قُلُوبِهِم مَّرَضٌ فَزَادَهُمُ ٱللَّهُ مَرَضًا ۖ وَلَهُمْ عَذَابٌ أَلِيمٌۢ بِمَا كَانُوا۟ يَكْذِبُونَ

In their hearts is disease, so Allāh has increased their disease; and for them is a painful punishment because they [habitually] used to lie.