Those who spend (freely) whether in prosperity or in adversity; who restrain their anger and pardon men; And Allah loves those who do good. (Noble Qur'an, 3:134)
Anger is a mental condition that provokes the excitement of man in words and deeds. Because of the dangers and sins such like mocking, gibe, obscenity, beating, killing, and the like evildoings - that are resulted from anger, it has been considered as the door to every evil.
According to Ibn Maskawayh, Anger, in fact, is an inner psychic movement due to which a state of agitation is produced in the heart's blood, arousing a desire for vengeance. And when this agitation becomes more violent, it intensifies the fire of anger. A violent commotion in the blood seizes the heart, filling the arteries and the brain with a flurry of dark smoke, on account of which the mind and the intellect lose control and become powerless.
Imam Muhammad al-Baqir (as) said: "Verily, anger is a spark ignited by the Shaitan (Satan) in the human heart. Indeed, when anyone of you gets angry, his eyes become red, the veins of his neck become swollen and Shaitan (Satan) enters them. Therefore, whosoever among you is concerned about himself on account of it, he should lie down for a while so that the filth of Shaitan (Satan) may be removed from him at the time."Anger is one of the conditions of the soul, and possesses three states.
1. The state of excess, which is defined as what would put one outside the bounds of religion and its laws.
2. The state of deficiency, which is defined as the state in which one 
fails to take a violent action even though it is necessary for his self defense.
fails to take a violent action even though it is necessary for his self defense.3. The state of moderation, in which anger is stimulated in appropriate and permissible circumstances. Thus it is clear that the first and the second states are amongst the vices of the soul, while the third is amongst ethical virtues produced by courage.
Excessive anger is a fatal disease, which can be considered as a type of temporary madness. When it subsides, it is immediately followed by remorse and repentance, which represent healthy responses of a rational person.
Amirul Muminin, Imam Ali (as) said: "Anger is a stroke of madness, since the afflicted later feels remorse and regrets. If someone does not feel any remorse after anger, it means that his madness has become fixed."
Amirul Muminin, Imam Ali (as) said: "Protect yourself from anger for its beginning is insanity and its end is remorse."
Moreover, absolute absence of anger is also a vice, which drags man into humiliation, subjugation and inability to defend his rights. In order to cure excessive anger, one must first remove its causes. These may be pride, selfishness, stubbornness, greed and other such vices. One must also consider how unseemly excessive anger is, and how evil its consequences may be. Secondly, he must examine the benefits of forbearance and self-restraint, and associate with people who possess these qualities. He must also realize that Allah's power is supreme, and everything is under His command, which would make him realize his own weakness compared with the infinite power of Allah. Thirdly, he should know that a person in a state of anger is not loved by Allah; moreover, he may do something in anger, of which he will be ashamed later on.
The opposite of anger is mildness and forbearance characteristics which count amongst perfect qualities of the soul. They make a person forgiving and merciful, although he may have complete power to take revenge.Keep to forgiveness, and enjoin what is fair, and turn away from the ignorant. (Noble Qur'an, 7:199)
And the Holy Prophet Muhammad (saw) said: "Forgiveness raises a man's station; forgive so that Allah (SWT) may honour you."
Islamic Sayings on Anger (Ghadab), Prophetic Sayings on Anger, Diseases of the Soul
The Holy Prophet Muhammad (saw) said: "Anger corrupts faith in the same way that vinegar destroys honey."
Imam Jafar Sadiq (as) narrated on the authority of his father Imam Muhammad al-Baqir (as) that a Bedouin came to the Holy Prophet Muhammad (saw) and said: "I live in the desert; hence, I want you to instruct me the comprehensive of speech." The Holy Prophet Muhammad (saw) said: "I instruct you not to be angry." As the Bedouin repeated the same request three times, the Holy Prophet Muhammad (saw) repeated the answer three times. The Bedouin commented: "I will not ask you for anything any more. Certainly, the Holy Prophet Muhammad (saw) has instructed me the best."
Imam Jafar Sadiq (as) said: "Anger is the key (that opens the door) to all kinds of vices."
Imam Jafar Sadiq (as) said: "A Mu'min (believer) is the person who when angered, his anger doesn't lead him away from that which is true."
Imam Muhammad al-Baqir (as) said: "A man often becomes so angry 
that he is never pleased until this causes him to be in Hell."
that he is never pleased until this causes him to be in Hell."The Attribute of Controlling Anger: Suppression of Anger, Diseases of the Soul
The behaviour of a courageous person is based on wisdom and serenity of soul. He gets angry on proper occasion and is patient and restrained. His anger is to the proper extent and if he takes revenge, it is with reason and discretion. He knows well as to whom he should forgive and what to overlook and ignore.
The anger of a true believer is for the sake of Allah (SWT). In the state of anger, he keeps in mind his duties, rights of creatures and never oppresses anyone. He neither makes the use of indecent language nor acts indiscreetly. All his acts are based on rational considerations and are in accordance with the norms of justice and Divine laws. He always acts in a way that he will not regret his actions later on.
Hence a true believer practices self-control and suppresses the motives of ill-temper through taking enough time before saying or doing anything.
The Holy Prophet Muhammad (saw) said: "The best Jihad is self-control."
The Holy Prophet Muhammad (saw) said: "He is not strong and powerful, who throws people down, but he is strong who withholds himself from anger."
The Holy Prophet Muhammad (saw) said: "Whoever suppresses his anger, when he has in his power to show it, Allah (SWT) will give him a great reward."
Amirul Muminin, Imam Ali (as) said: "The most powerful person is the one who is victorious over his anger with his forbearance."Amirul Muminin, Imam Ali (as) said: "When a person gets angry, if he is standing, he should immediately lie down (sit down) on earth for a while as this removes the filth of Shaitan (Satan) from him at that time."
Amirul Muminin, Imam Ali (as) said: "Keep off anger because it is one large army from the Shaitan's (Satan) armies."
Imam Jafar Sadiq (as) said: "One who refrains his anger (towards someone), Allah (SWT) will cover his secrets."
Imam Muhammad al-Baqir (as) said: "Any one who suppresses his anger, Allah (SWT) will add to his honour and authority in this world and the world to come."
Anger Management in Islam: A Hole in the Fence, Anger (Ghadab), Bad Temper, Human Vices
There once was a little boy who had a bad temper (anger). His Father gave him a bag of nails and told him that every time he lost his temper and get angry, he must hammer a nail into the back of the fence.
The first day the little boy had driven 37 nails into the fence. Over the next few weeks, as he learned to control his anger, the number of nails hammered daily gradually dwindled down.
Little boy discovered it was easier to hold his temper (anger) than to drive those nails into the fence...
Finally the day came when the little boy did not lose his temper (anger) at all. He told his father about it and the father suggested that the little boy now pull out one nail for each day that he was able to hold his temper (anger). The day passed and the little boy was finally able to tell his father that all the nails were gone.
The father took his little boy by the hand and led him to the fence. He said, "You have done well, my son, but look at the holes in the fence.
The fence will never be the same. When you say things in anger, they leave a scar just like this one. You can put a knife in a man and draw it out. It won't matter how many times you say I'm sorry, the wound is still there."
Our Holy Prophet Muhammad (saw) mentions the tongue before the hand. As everybody knows, the 'wounds' caused by the tongue are deeper and more hurtful than those caused by the hand. Besides, one is often prepared to strike more readily, easily and more frequently with one's tongue than with the hand. Slandering, backbiting, reproaching and other similar ways of hurting people are commoner and more difficult to avoid than hurt done by the hand. Further, if a person can refrain from hurting with the tongue, he can more easily refrain from the assaults by the hand. Again, defending oneself against physical assaults is, in most cases, easier than against verbal assaults of, in particular, backbiting and slandering. So, a true Muslim always restrains his tongue as well as his hand from hurting others.
