I Samuel 19:4-6

Thus Jonathan spoke well of David to Saul his father, and said to him, “Let not the king sin against his servant, against David, because he has not sinned against you, and because his works have been very good toward you. For he took his life in his hands and killed the Philistine, and the LORD brought about a great deliverance for all Israel. You saw it and rejoiced. Why then will you sin against innocent blood, to kill David without a cause?” So Saul heeded the voice of Jonathan, and Saul swore, “As the LORD lives, he shall not be killed.”