AGAINST ANGER Someone told the following incident from Isaac the monk's life:

Once, he says, I quarreled with my brother and became angry with him. Meanwhile, sitting doing my needlework, I remembered my quarrel, repented and, worried by the fear of responsibility before God, thought: what should I do? At that time a young man came to me and, not making, as it were, a sign of the cross, said: "You have sinned and are worried; surrender yourself to me and you will be at peace. " I, after learning that it was the devil, answered: "Go away, for you are not from God." He told me: "I'm sorry for you: you're ruining your cause, but still you are mine." "No," I say, "I'm not yours, the devi's, but God's." He said: "Those holding on to wrath and who remember evil done God has given to us; you have been angry with your brother for three weeks. " I answered: "You're lying." And he: 
"You have evil on him; and those who hold grudges expect a fire from Gehenna, and I am put to such people, and you are mine. " Hearing this, I immediately went to my brother, bowed to him and reconciled with him. What? Returning home, I saw that the devil, not tolerating my reconciliation, out of malice burned my handicraft and matting, which I usually underpinned when I prayed.
From this narrative you see, brethren, that whoever has anger against one's neighbor, the enemy of our salvation has the closest access to him, the devil; that whoever does not repent of his malice, the devil acquires even more power; that the Gehenna fire awaits in the Afterlife who are holding on to malice; and that, finally, by repenting in our anger and reconciliation with our neighbors, we disgrace the devil and drive him away from ourselves. 
Knowing this, what should we do, brethren? Sparks of anger must be extinguished in the heart at the very beginning, so that the spark does not turn into a flame and after it does not turn into a Gehenna flame. We must forgive offenses and love our enemies. And in order to get a handle on this, we will, first, often think about our guilt before God and about the mercy of God to us sinners.