Right and wrong anger

A brother asked Abba Poemen, "What is the meaning of the text, 'Whoever is angry with his brother without a cause' (Matthew 5:22)?" He answered, "If you are angry with your brother for any kind of trouble that he gives you, that is anger without a cause, and it is better to pluck out your right eye and cast it from you. But if anyone wants to separate you from God, then you must be angry with him." (from the sayings of the Desert Fathers)