Surah Al-Baqarah — Ayah 6 (2:6)
إِنَّ ٱلَّذِينَ كَفَرُواْ سَوَآءٌ عَلَيۡهِمۡ ءَأَنذَرۡتَهُمۡ أَمۡ لَمۡ تُنذِرۡهُمۡ لَا يُؤۡمِنُونَ ٦
English translation (Saheeh International)
Indeed, those who disbelieve1 - it is all the same for them whether you warn them or do not warn them - they will not believe.
- - Literally, "cover" or "conceal" (faith or truth).
Brief commentary
Those who reject what Allah revealed to His Messenger continue on the wrong path in their stubbornness. So, it makes no difference whether you warn them or not.