10 Holy Job, himself also powerful in this world, says: “I hid not my sin, but declared it before all the people.” His son Jonathan said to the fierce King Saul himself: “Do not sin against your servant David;” and: “Why do you sin against innocent blood, to slay David without a cause?” For, although he was a king, yet he would have sinned if he slew the innocent. And again, David also, when he was in possession of the kingdom, and had heard that innocent Abner had been slain by Joab, the leader of his host, said: “I am guiltless and my kingdom is guiltless henceforth and for ever of the blood of Abner, the son of Ner,” and he fasted for sorrow.
Source: Letters (New Advent)