以 子 之 矛 攻 子 之 盾

以子之矛，攻子之盾

以子之矛，攻子之盾

yi3 zi3 zhi1 mao2 , gong1 zi3 zhi1 dun4

lit. use sb's spear to attack his shield (idiom, derived from Han Feizi 韓非子|韩非子); turning a weapon against its owner fig. to attack an opponent using his own devices hoist with his own petard