1 Samuel 17:39-40

And David girded his sword upon his apparel, and he assayed to go; for he had not proved it. And David said unto Saul, I cannot go with these; for I have not proved them. And David put them off him. And he took his staff in his hand, and chose him five smooth stones out of the brook, and put them in the shepherd’s bag which he had, even in his wallet; and his sling was in his hand: and he drew near to the Philistine.