I Samuel 27:1-2

And David said in his heart, “Now I shall perish someday by the hand of Saul. There is nothing better for me than that I should speedily escape to the land of the Philistines; and Saul will despair of me, to seek me anymore in any part of Israel. So I shall escape out of his hand.” Then David arose and went over with the six hundred men who were with him to Achish the son of Maoch, king of Gath.