1 Samuel 17:39 in the King James Version
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.
Context
38 Saul dressed David with his clothing. He put a helmet of bronze on his head, and he clad him with a coat of mail.
39 David strapped his sword on his clothing and he tried to move, for he had not tested it. David said to Saul, “I can’t go with these, for I have not tested them.” Then David took them off.
40 He took his staff in his hand, and chose for himself five smooth stones out of the brook, and put them in the pouch of his shepherd’s bag which he had. His sling was in his hand; and he came near to the Philistine.