I suppose it should come as no surprise that the Bible has a great deal to say about anger. Anger is, after all, not only a result of sin but also a common cause of sin. Here is what the Bible has to say:
It is good to be slow to anger. Those who are quick to anger display a lack of wisdom.
Whoever is slow to anger has great understanding, but he who has a hasty temper exalts folly. (Proverbs 14:29)
Know this, my beloved brothers: let every person be quick to hear, slow to speak, slow to anger. (James 1:19)
Be not quick in your spirit to become angry, for anger lodges in the heart of fools. (Ecclesiastes 7:9)
Anger should be addressed as soon as possible because it can easily turn to sin.
The LORD said to Cain, “Why are you angry, and why has your face fallen? If you do well, will you not be accepted? And if you do not do well, sin is crouching at the door. Its desire is for you, but you must rule over it.” (Genesis 4:6-7)
You have heard that it was said to those of old, “You shall not murder; and whoever murders will be liable to judgment.” But I say to you that everyone who is angry with his brother will be liable to judgment …. So if you are offering your gift at the altar and there remember that your brother has something against you, leave your gift there before the altar and go. First be reconciled to your brother, and then come and offer your gift. (Matthew 5:21-24)
Be angry and do not sin; do not let the sun go down on your anger. (Ephesians 4:26)
Though at times anger can be righteous (see especially Mark 3:5 where Jesus becomes angry), anger is generally to be avoided.
For I fear that perhaps when I come I may find you not as I wish, and that you may find me not as you wish—that perhaps there may be quarreling, jealousy, anger, hostility, slander, gossip, conceit, and disorder. (2 Corinthians 12:20)
Now the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God. (Galatians 5:19-21)
Let all bitterness and wrath and anger and clamor and slander be put away from you, along with all malice. (Ephesians 4:31)
But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth. (Colossians 3:8)
Know this, my beloved brothers: let every person be quick to hear, slow to speak, slow to anger; for the anger of man does not produce the righteousness of God. (James 1:19-20)