猫鼠同眠（貓鼠同眠）　

◎ 猫鼠同眠 māoshǔ-tóngmián

[thieves and police work together,as the cat and the rat sleep together;act in collusion with each other] 比喻官吏失职,纵容坏人,也比喻上下勾结,朋比为奸(一个使的丫头,和他猫鼠同眠,惯的有些折儿!——《金瓶梅词话》)