1 Samuel 24:17-22

17“You are more righteous than I,” he said. “You have treated me well, but I have treated you badly. 18You have just now told me about the good you did to me; the Lord delivered me into your hands, but you did not kill me. 19When a man finds his enemy, does he let him get away unharmed? May the Lord reward you well for the way you treated me today. 20I know that you will surely be king and that the kingdom of Israel will be established in your hands. 21Now swear to me by the Lord that you will not kill off my descendants or wipe out my name from my father’s family.” 22So David gave his oath to Saul. Then Saul returned home, but David and his men went up to the stronghold.