1 Samuel 17:38-42

Then Saul clothed David with his military attire and put a bronze helmet on his head, and outfitted him with armor.

And David strapped on his sword over his military attire and struggled at walking, for he had not trained with the armor. So David said to Saul, “I cannot go with these, because I have not trained with them.” And David took them off.

Then he took his staff in his hand and chose for himself five smooth stones from the brook, and put them in the shepherd’s bag which he had, that is, in his shepherd’s pouch, and his sling was in his hand; and he approached the Philistine.

Then the Philistine came and approached David, with the shield-bearer in front of him.

When the Philistine looked and saw David, he was contemptuous of him; for he was only a youth, and reddish, with a handsome appearance.