[ jiāng shān yì gǎi，bǐng xìng nán yí ]

人的本性的改变，比江山的变迁还要难。形容人的本性难以改变。

明·冯梦龙《醒世恒言》第三十五卷：“看官有所不知。常言道得好，江山易改，禀性难移。”

It's easy to change rivers and mountains but hard to change a person's nature;a fox may grow grey,but never good;a sow,when washed,returns to the muck;it is hard to change man's natural disposition than to change rivers and mountains