Al-Hujurat · 49:9

9. O believers! If two groups of believers quarrel with one another, then reconcile between them by inviting them to let the law of Allah be the judgement between them. Then, if one of the two reject the reconciliation and transgresses, fight the transgressing group until it returns to accepting the command of Allah. If it returns, reconcile between the two groups with fairness and justice. And be fair in your judgement between them, indeed, Allah loves those who are fair in their judgement.