1 Samuel 17:29-33

And David said, What have I now done? Is there not a cause? And he turned from him toward another, and spake after the same manner: and the people answered him again after the former manner. And when the words were heard which David spake, they rehearsed them before Saul: and he sent for him. And David said to Saul, Let no man's heart fail because of him; thy servant will go and fight with this Philistine. And Saul said to David, Thou art not able to go against this Philistine to fight with him: for thou art but a youth, and he a man of war from his youth.