So Saul heeded the voice of Jonathan, and Saul swore, "As the LORD lives, he shall not be killed."
1 Samuel 19:6
Surrounding context
19:5 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?"
19:6 So Saul heeded the voice of Jonathan, and Saul swore, "As the LORD lives, he shall not be killed."
19:7 Then Jonathan called David, and Jonathan told him all these things. So Jonathan brought David to Saul, and he was in his presence as in times past.