Hamlet:
I do repent; but heaven hath pleas'd it so
To punish me with this, and this with me,
That I must be their scourge and minister.
I will bestow him, and will answer well
The death I gave him.
So again good night.
I must be cruel only to be kind.
This bad begins and worse remains behind.

Hamlet Act 3, scene 4, 173 - 179