1 Samuel 28:1-2

Now in those days the Philistines gathered their forces for war to fight against Israel. So Achish said to David, “Certainly you realize that you must go out with me in the army, you and your men.” David said to Achish, “Very well, you will know what your servant can do.” Achish said to David, “Very well, I will make you my bodyguard for life.”