1 Samuel 17:39-40

39And David strapped on his sword over his military attire and struggled at walking, for he had not trained with the armor. So David said to Saul, “I cannot go with these, because I have not trained with them.” And David took them 1off. 40Then he took his staff in his hand and chose for himself five smooth stones from the brook, and put them in the shepherd’s bag which he had, that is, in his shepherd’s pouch, and 2his sling was in his hand; and he approached the Philistine.