Anger is the key to all evil.

A man said to the Prophet, ‘Give me advice.’ The Prophet, peace be upon him, said, ‘Do not get angry.’ The man asked repeatedly, and the Prophet answered each time, ‘Do not get angry.’
(Sahih al-Bukhari, Hadith – 6116)

Dear brothers and sisters,
Anger is built-in to all people so that it can be used as a weapon to defend people from any kind of harm. But when anger is used against intellect, it becomes harmful. Most of the people can’t perfectly use their anger in time. So anger became the cause of their failure. Anybody can become angry – that is easy, but to be angry with the right person and to the right degree and at the right time and for the right purpose, and in the right way – that is not within everybody’s power and is not easy.
In the above-mentioned Hadith, “Do not get angry” doesn’t mean that it is impermissible to have any sort of anger, because that would be outside human ability. There is a rule in Usul al-fiqh which states that it is not permissible for someone to be held accountable for that which he can’t control. Anger is part of human nature. The real question is, what is the permissible level of anger? How can we handle that anger when we do become angry? When the Prophet (PBUH) insisted on not getting angry, he implied that controlling one’s anger is a comprehensive act. Anger opens the door to all bad qualities and staying away from it opens the door to all good qualities. One of the Prophet’s companions said, “Anger is the key to all evil.”
There are many harmful effects of getting angry. These effects can harm us physically, psychologically, socially or emotionally. It is well known today that anger causes many health problems and can be a symptom or cause of mental illness, especially if not controlled. It’s so important to realize that every time you get upset, it drains your emotional energy. Losing your cool makes you tired. Getting angry a lot messes with your health and mind. Anger is the cause of failure.
Jobayer Al Mahmud, Uludag University, Bursa, Turkey