1 Samuel 17:39-40

39David fastened his sword to his armor and tried to walk, for he had not tested them. And David said to Saul, “I cannot walk with these, for I have not tested them.” So David took them off.

40Then he took his staff in his hand; and he chose for himself five smooth stones from the brook, and put them in a shepherd’s bag, in a pouch which he had, and his sling was in his hand. And he drew near to the Philistine.