2 Samuel 20

2 Samuel 20:9-10

Would you like that, in another way also, I should make what I say plainer? Let us look into their case, [to those] who avenge themselves even justly. For concerning the wrongdoers, that they are the most worthless of all people, warring against their own soul, is surely plain to every one.But who avenged himself justly yet kindled innumerable ills and pierced himself through with many calamities and sorrows? The captain of David's host. For Joab both stirred up a grievous war and suffered unnumbered evils; not one of them would have happened had he but known how to exercise self-control. Let us flee therefore from this sin and neither in words nor deeds do our neighbors wrong. — HOMILIES ON THE GOSPEL OF MATTHEW 42.2