Sirach 28: 1 - 7
1 He that takes vengeance will suffer vengeance from the Lord, and he will firmly establish his sins.
2 Forgive your neighbor the wrong he has done, and then your sins will be pardoned when you pray.
3 Does a man harbor anger against another, and yet seek for healing from the Lord?
4 Does he have no mercy toward a man like himself, and yet pray for his own sins?
5 If he himself, being flesh, maintains wrath, who will make expiation for his sins?
6 Remember the end of your life, and cease from enmity, remember destruction and death, and be true to the commandments.
7 Remember the commandments, and do not be angry with your neighbor; remember the covenant of the Most High, and overlook ignorance.

EWTN