同恶相济（同惡相濟）　

◎ 同恶相济 tóng’è-xiāngjì

[sharing the evil and assisting the cause;the wicked support the wicked] 同是恶人而彼此互相济助,为非作歹

暨诸葛诞滔天作逆,称兵扬 楚,钦咨捕罪,同恶相济。——《晋书》