1 Samuel 17:38-39

Then Saul dressed David in his garments and put a bronze helmet on his head, and put a coat of mail (armor) on him. Then David fastened his sword over his armor and tried to walk, [but he could not,] because he was not used to them. And David said to Saul, “I cannot go with these, because I am not used to them.” So David took them off.