1 Samuel 17:38-40

Then Saul outfitted David as a soldier in armor. He put his bronze helmet on his head and belted his sword on him over the armor. David tried to walk but he could hardly budge. David told Saul, “I can’t even move with all this stuff on me. I’m not used to this.” And he took it all off. Then David took his shepherd’s staff, selected five smooth stones from the brook, and put them in the pocket of his shepherd’s pack, and with his sling in his hand approached Goliath.