I Samuel 17:14-19

David was the youngest. And the three oldest followed Saul. But David occasionally went and returned from Saul to feed his father’s sheep at Bethlehem. And the Philistine drew near and presented himself forty days, morning and evening. Then Jesse said to his son David, “Take now for your brothers an ephah of this dried grain and these ten loaves, and run to your brothers at the camp. And carry these ten cheeses to the captain of their thousand, and see how your brothers fare, and bring back news of them.” Now Saul and they and all the men of Israel were in the Valley of Elah, fighting with the Philistines.