1 Samuel 28:1-2

Around that time the Philistines called up their armies to go to war against Israel. So Achish told David, “You do realize that you and your men must accompany me as part of the army.” “That's fine!” David replied. “Then you yourself will discover what I, your servant, can do.” “That's fine too,” Achish responded. “I'll make you my bodyguard for life.”