1 Samuel 28:1-2

And it cometh to pass in those days, that the Philistines gather their camps for the war, to fight against Israel, and Achish saith unto David, ‘Thou dost certainly know that with me thou dost go out into the camp, thou and thy men.’ And David saith unto Achish, ‘Therefore — thou dost know that which thy servant dost do.’ And Achish saith unto David, ‘Therefore — keeper of my head I do appoint thee all the days.’