'Then Jonathan told David, “I promise by the Lord , the God of Israel, that by this time tomorrow, or the next day at the latest, I will talk to my father and let you know at once how he feels about you. If he speaks favorably about you, I will let you know. But if he is angry and wants you killed, may the Lord strike me and even kill me if I don’t warn you so you can escape and live. May the Lord be with you as he used to be with my father. '
1 Samuel 20:12-13