两败俱伤

liǎngbài-jùshāng

[internecine; both parties be weakened by mutual homicide; both being defeated and wounded; both sides suffer; cut one another's throat; neither side gains] 争斗的双方都受到损失

倘若大人再要回护他三人, 将来一定两败俱伤, 于大人反为无益。 --清·李宝嘉《官场现形记》