Proverbs 29:22

An angry man stirreth up strife, and a furious man aboundeth in transgression.

The verse belongs to chapters 25 to 29, the collection of Solomon's proverbs copied out by men appointed by Hezekiah.
That collection was compiled about three hundred years after Solomon.
It is a short, pointed saying that states a familiar truth.

An angry person is sure to act foolishly and do harmful things that give opponents an advantage over him.
A single fit of anger can do harm that follows a person all his lifetime, and those who witness it will not forget it.
Overlooking such anger and loving the offender just as much as before takes very deep and strong love, a forbearance people generally will not show.