1 Samuel 28:2 in the King James Version
And David said to Achish, Surely thou shalt know what thy servant can do. And Achish said to David, Therefore will I make thee keeper of mine head for ever.
Context
1 In those days, the Philistines gathered their armies together for warfare, to fight with Israel. Achish said to David, “Know assuredly that you will go out with me in the army, you and your men.”
2 David said to Achish, “Therefore you will know what your servant can do.” Achish said to David, “Therefore I will make you my bodyguard forever.”
3 Now Samuel was dead, and all Israel had mourned for him and buried him in Ramah, even in his own city. Saul had sent away those who had familiar spirits and the wizards out of the land.