It was narrated that Abu Hurayrah (may Allah be pleased with him) said: 

Humaid bin Abdul Rahman narrated on the authority of one of the companions of the Prophet (peace and blessings of Allah be upon him) said: A man said: O Messenger of Allah advise me. He (peace and blessings of Allah be upon him) said: "Do not get angry." He said: I reflected on the saying of the Messenger of Allah (peace and blessings of Allah be upon him) and found that anger combines all the sorts of evil. Compiled by Ahmad and classed as Saheeh by Al AlbaniIt was narrated that Ibn 'Umar (may Allah be pleased with them) asked the Messenger of Allah (peace and blessings of Allah be upon him): What is the deed that can keep me distant from the wrath of Allah? He (peace and blessings of Allah be upon him) said: "Do not get angry." compiled by Ahmad and Ibn Hibban in Saheeh"; but with the phrase what protects me …

There are many Hadiths that bears this commandment: do not get angry.

This commandment is a great piece of wisdom issued by a wise man on whose heart the springs of wisdom burst out till its seekers relinquished and led a good life away from the evil; its causes and motives. they lived to the wisdom and then reflect its meanings and goals to enjoy the fruits obtained through meditation and looking at its effects.

The companions, may Allah be pleased with them, used to come to the Prophet (peace and blessings of Allah be upon him) asking him for advice since they know that his commandments are healing medicines for the diseases of the believing souls and the conscious hearts.

The believing souls respond to these commandments, find rest and absorb easily. Therefore, they benefit greatly in the elimination of the fanaticism of ignorance and the evil inherited customs, so that these souls turn from commanding with evil to blaming and regretting souls which do not insist on the sin, or belittle it rather they take the initiative to repent from it.