1 Samuel 17:39-40

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.