The Quran

وَإِن طائِفَتانِ مِنَ المُؤمِنينَ اقتَتَلوا فَأَصلِحوا بَينَهُما ۖ فَإِن بَغَت إِحداهُما عَلَى الأُخرىٰ فَقاتِلُوا الَّتي تَبغي حَتّىٰ تَفيءَ إِلىٰ أَمرِ اللَّهِ ۚ فَإِن فاءَت فَأَصلِحوا بَينَهُما بِالعَدلِ وَأَقسِطوا ۖ إِنَّ اللَّهَ يُحِبُّ المُقسِطينَ

Muhammad Asad

Hence, if two groups of believers fall to fighting,¹ make peace between them; but then, if one of thetwo [groups] goes on acting wrongfully towards the other, fight against the one that acts wrongfully until it reverts to God's commandment;² and if they revert, make peace between them with justice, and deal equitably [with them]: for verily, God loves those who act equitably!

The expression "fighting" comprises in this context all modes of discord and contention, both in word and deed, evidently as a consequence of the slanderous rumours spoken of in verse 6 above.
I.e., that the believers should act as brethren (see next verse).