Quran 9:125

وَأَمَّا ٱلَّذِينَ فِى قُلُوبِهِم مَّرَضٌ۬ فَزَادَتۡہُمۡ رِجۡسًا إِلَىٰ رِجۡسِهِمۡ وَمَاتُواْ وَهُمۡ ڪَـٰفِرُونَ ١٢٥

As for those who harbored doubts in their hearts, it actually added unholiness to their unholiness, and they died as disbelievers.