1 Samuel 17:39-40

39David strapped his sword on his garment and tried to walk, but he was not used to it. So David said to Saul, “I cannot walk in these, for I am not used to them.” So David took them off.

40Then he took his staff in his hand, chose five smooth stones from the valley, put them in the pocket of the shepherd’s bag that he had, and with his sling in his hand, he approached the Philistine.