Being the king of Israel, Saul would have had the general loyalty of most people living in the land. With David residing in the vicinity of Adullam and having gathered a number of men to him, he was bound to be discovered. News of his whereabouts would have gradually spread to finally arrive in the ears of Saul.1
6 Now Saul heard that David was discovered, and the men who were with him. Saul was sitting at Gibeah under the tamarisk tree on the height with his spear in his hand, and all his servants were standing about him.