Anger in the Quran and Hadith
Allah mentions as one of the qualities of the Muttaqeen, the God-conscious, that they control their anger:

“Those who spend (in Allah’s cause) in prosperity and in adversity, who repress their anger, and who pardon men, verily, Allah loves the al-Muhsinun (the good-doers).” (3:134)

“Don’t become 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 (sas) 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.”