Indeed, those who disbelieve - it is all the same for them whether you warn them or do not warn them - they will not believe.  

إِنَّ الَّذِينَ كَفَرُوا سَوَاءٌ عَلَيْهِمْ أَأَنْذَرْتَهُمْ أَمْ لَمْ تُنْذِرْهُمْ لَا يُؤْمِنُونَ  

Allah has set a seal upon their hearts and upon their hearing, and over their vision is a veil. And for them is a great punishment.  

خَتَمَ اللَّهُ عَلَىٰ قُلُوبِهِمْ وَعَلَىٰ سَمْعِهِمْ ۖ وَعَلَىٰ أَبْصَارِهِمْ غِشَاوَةٌ ۖ وَلَهُمْ عَذَابٌ عَظِيمٌ