Surah At-Taubah (The Repentance), Verse 12

وَاِنْ نَّكَثُوْۤا اَیْمَانَهُمْ مِّنْ بَعْدِ عَهْدِهِمْ وَطَعَنُوْا فِیْ دِیْنِكُمْ فَقَاتِلُوْۤا اَىِٕمَّةَ الْكُفْرِ اِنَّهُمْ لَاۤ اَیْمَانَ لَهُمْ لَعَلَّهُمْ یَنْتَهُوْنَ ۟

Wa in nakasooo aimaanahum mim ba'di 'ahdihim wa ta'anoo fee deenikum faqaatilooo a'immatal kufri innahum laaa aimaana lahum la'allahum yantahoon

“But if they violate their oaths after their covenant, and taunt you for your Faith,- fight ye the chiefs of Unfaith: for their oaths are nothing to them: that thus they may be restrained.”

Quran 9:12 (Yusuf Ali Translation)