1 Samuel 17:38-40 (KJV)
38 And Saul armed David with his armour, and he put an helmet of brass upon his head; also he armed him with a coat of mail.
39 And David girded his sword upon his armour, 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.
40 And he took his staff in his hand, and chose him five smooth stones out of the brook, and put them in a shepherd’s bag which he had, even in a scrip; and his sling was in his hand: and he drew near to the Philistine.