1 Samuel 24:13 - Ellicott's Commentary On The Whole Bible

The proverb of the ancients. — Clericus, quoted by Lange, explains these words: “David means to say, that if he had been guilty of conspiracy against the king, he would not have neglected this favourable opportunity to kill him, since men usually indulge their feelings, and from a mind guilty of conspiracy nothing but corresponding deeds could come forth.” So Grotius, who writes how “actions usually correspond to the quality of the mind.” Erdmann quotes a Greek proverb: “From a bad raven comes a bad egg.”