‘In your anger do not sin’: do not let the sun go down while you are still angry,and do not give the devil a foothold.  (Ephesians 4:26-27 NIV)

Many deem anger to be a sin, so to what does Paul elude here?  Actually, he quotes from the Septuagint:

Answer me when I call, O God of my righteousness!
    You have given me relief when I was in distress.
    Be gracious to me and hear my prayer!
O men, how long shall my honour be turned into shame?
    How long will you love vain words and seek after lies? Selah
But know that the Lord has set apart the godly for himself;
    the Lord hears when I call to him.
Be angry, and do not sin;
    ponder in your own hearts on your beds, and be silent. (Psalm 4:1-4)

David is crying out to God but also pleading with his enemies (possibly rhetorically).  He is asking them to bear their anger and not act upon it.  And it is this that Paul reiterates to the man and woman now set apart in Christ to deal differently with anger, knowing full well that any opposition, prejudice or persecution will provoke anger.