I Samuel 17:12-21

Now David was the son of that Ephrathite of Bethlehem Judah, whose name was Jesse, and who had eight sons. And the man was old, advanced in years, in the days of Saul. The three oldest sons of Jesse had gone to follow Saul to the battle. The names of his three sons who went to the battle were Eliab the firstborn, next to him Abinadab, and the third Shammah. 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. So David rose early in the morning, left the sheep with a keeper, and took the things and went as Jesse had commanded him. And he came to the camp as the army was going out to the fight and shouting for the battle. For Israel and the Philistines had drawn up in battle array, army against army.