翻译：中国有句老话，对敌人的仁慈就是对自己的残忍。

There is an old Chinese saying, 'Mercy to foes is cruelty to yourself.'
--绝对正确，楼上几位有点小语法错误。

There is an old saying in China, to the enemy's mercy is for their owe cruel.

There is an old Chinese saying : Being merciful to your enemy is being cruel to your ownself.

there is an old Chinese saying goes, "show mercy to foe is be cruel to self"