a tooth for a tooth 以牙还牙；以眼还眼

【例句】
You should deal with your enemy by following the rule of eye for an eye and a tooth for a tooth.
对敌人你应该以眼还眼，以牙还牙。

We should forgive people who hurt us, not following the role of eye for an eye and a tooth for a tooth.
我们应该原谅伤害过我们的人，不应该以眼还眼，以牙还牙。