1 Samuel 17:38-41

38Then Saul dressed David in his own tunic. He put a coat of armor on him and a bronze helmet on his head.

39David fastened on his sword over the tunic and tried walking around, because he was not used to them. “I cannot go in these,” he said to Saul, “because I am not used to them.” So he took them off.

40Then he took his staff in his hand, chose five smooth stones from the stream, put them in the pouch of his shepherd’s bag and, with his sling in his hand, approached the Philistine. 41Meanwhile, the Philistine, with his shield bearer in front of him, kept coming closer to David.