From his Sermon On Soberness And Moderation Against Gluttony And Drunkenness (1539).

In Christianity it must not happen that one person should hurt another, in the same way that the members of the body, the teeth, tongue, toes, fingers, hands, eyes, touch each other without hurting each other. It is true, of course, that even among Christians life does not go on without offenses being committed. You have only to look at husband and wife in the family. Some times a word is uttered or something is done which angers the husband or the wife. But when this is done to a neighbor, then gestures are made which make people angry and the man’s relatives Come seeking revenge and are not satisfied until the offense has been repaid tenfold. So you must have a strong love, which is best able to cover up sins.

Also consider what Solomon said: “Hatred stirs up strife, but love covers all offenses” [Prov. 10:12]. This is how you should deal with your neighbor. If you do not do this, He will remove his cover. This is what Paul means when he says, “Bear one another’s burdens, and so fulfil the law of Christ” [Gal. 6:2]. But the Holy Spirit has sanctified you through faith and given you love, in order that you may bear with others. Christ has borne your sins, in order that you may bear with the sins of others.

So in worldly affairs, too; one rubs against the other. Here, too, you must not become angry and be ready to do harm. Rather be content if someone possesses the same thing you have and do not be envious. If anybody speaks against you, you say: May God forgive him. If you are a Christian, your neighbor will not make you so angry that you would do him injury. If you do, then there is no love.

Luther, M. (1999). Vol. 51: Luther’s works, vol. 51: Sermons I (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.) (297–298). Philadelphia: Fortress Press.