Surah Al-Hujurat (The Private Quarters), Verse 9

وَاِنْ طَآىِٕفَتٰنِ مِنَ الْمُؤْمِنِیْنَ اقْتَتَلُوْا فَاَصْلِحُوْا بَیْنَهُمَا فَاِنْ بَغَتْ اِحْدٰىهُمَا عَلَی الْاُخْرٰی فَقَاتِلُوا الَّتِیْ تَبْغِیْ حَتّٰی تَفِیْٓءَ اِلٰۤی اَمْرِ اللّٰهِ فَاِنْ فَآءَتْ فَاَصْلِحُوْا بَیْنَهُمَا بِالْعَدْلِ وَاَقْسِطُوْا اِنَّ اللّٰهَ یُحِبُّ الْمُقْسِطِیْنَ ۟

Wa in taaa'ifataani minal mu'mineena naqtataloo fa aslihoo bainahumaa; fa-im baghat ihdaahumaa 'alal ukhraa faqaatilul latee tabghee hattaa tafeee'a ilaaa amril laah; fa-in faaa'at fa aslihoo bainahumaa bil'adli wa aqsitoo, innal laaha yuhibbul muqsiteen

“If two parties among the Believers fall into a quarrel, make ye peace between them: but if one of them transgresses beyond bounds against the other, then fight ye (all) against the one that transgresses until it complies with the command of Allah; but if it complies, then make peace between them with justice, and be fair: for Allah loves those who are fair (and just).”

Quran 49:9 (Yusuf Ali Translation)