1 Samuel 17:15-19

but David went back and forth from Saul to tend his father’s flock at Bethlehem.

And the Philistine came forward morning and evening, and took his stand for forty days.

Then Jesse said to his son David, “Take now for your brothers an ephah of this roasted grain and these ten loaves, and run to the camp to your brothers.

Bring also these ten slices of cheese to the commander of their thousand, and look into the well-being of your brothers and bring back confirmation from them.

For Saul and they and all the men of Israel are in the Valley of Elah, fighting the Philistines.” David Accepts the Challenge