He who does not punish evil invites it.
More German Proverbs:
What! keep a dog and bark myself?German
Who bows to might loses his right.
German
Who stands bail for someone is being teased by the devil.
German
The unexpected always happens.
German
Little folks are fond of talking about what great folks do.
German
Promises may make friends, but 'tis performances that keep them.
German