Not to do evil

This was a conversation between Socrates and his student Crito when Socrates was in prison awaiting his final moments.... Socrates was teaching in his classic 'I question you and you think out the answer yourself' manner"

SOCRATES: Then we must do no wrong?

CRITO: Certainly not.

SOCRATES: Nor when injured injure in return, as the many imagine; for we must injure no one at all?

CRITO: Clearly not.

SOCRATES: Again, Crito, may we do evil?

CRITO: Surely not, Socrates.

SOCRATES: And what of doing evil in return for evil, which is the morality of the many—is that just or not?

CRITO: Not just.

SOCRATES: For doing evil to another is the same as injuring him?

CRITO: Very true.

SOCRATES: Then we ought not to retaliate or render evil for evil to any one, whatever evil we may have suffered from him.

And Socrates concludes one of his final lessons for Humanity in saying

"It is never right to do wrong and never right to take revenge, nor is it right to give evil, or in the case of one who has suffered some injury, to attempt to get even"