Surah At-Taubah (The Repentance), Verse 80

اِسْتَغْفِرْ لَهُمْ اَوْ لَا تَسْتَغْفِرْ لَهُمْ اِنْ تَسْتَغْفِرْ لَهُمْ سَبْعِیْنَ مَرَّةً فَلَنْ یَّغْفِرَ اللّٰهُ لَهُمْ ذٰلِكَ بِاَنَّهُمْ كَفَرُوْا بِاللّٰهِ وَرَسُوْلِهٖ وَاللّٰهُ لَا یَهْدِی الْقَوْمَ الْفٰسِقِیْنَ 

istaghfir lahum aw laa tastaghfir lahum in tastaghfir lahum sab'eena marratan falany yaghfiral laahu lahum; zaalika bi annahum kafaroo billaahi wa Rasoolih; wallaahu laa yahdil qawmal faasiqeen

“Whether thou ask for their forgiveness, or not, (their sin is unforgivable): if thou ask seventy times for their forgiveness, Allah will not forgive them: because they have rejected Allah and His Messenger: and Allah guideth not those who are perversely rebellious.”

Quran 9:80 (Yusuf Ali Translation)