两败俱伤（兩敗俱傷）　

◎ 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》