1 Samuel 17:38-40 New Revised Standard Version (NRSV)
38 Saul clothed David with his armor; he put a bronze helmet on his head and clothed him with a coat of mail. 39 David strapped Saul’s sword over the armor, and he tried in vain to walk, for he was not used to them. Then David said to Saul, “I cannot walk with these; for I am not used to them.” So David removed them. 40 Then he took his staff in his hand, and chose five smooth stones from the wadi, and put them in his shepherd’s bag, in the pouch; his sling was in his hand, and he drew near to the Philistine.