DO NOT DO EVEN A SLIGHT WRONG
Akatam dukkatam seyyo paccha tapati dukkatam
Katan ca sukatam seyyo yam katva n'anutappati.
It is better not to do an evil deed; an evil deed torments one later on. It is better to do a good deed as one does not grieve for having done it. 
Once, a woman with a very strong sense of jealousy lived with her husband in Savatthi. She found out that her husband was having an affair with her maid. So one day, out of anger, she tied up the maid, cut off her ears and nose and shut her up in a room. After doing that, she accompanied her husband to the Jetavana monastery. Soon after they left, some relatives of the maid arrived at their house and found the maid tied up and locked up in a room. They freed her and took her to the monastery. The maid related to the Buddha what her mistress had done to her. She stood in the midst of the crowd for all to see how she had been tortured. So the Buddha said, 'Do no evil, thinking that people will not know about it. An evil deed done in secret, when discovered, will bring much pain and sorrow. But a good deed may be done secretly, for it can only bring happiness and not sorrow.'
The jealous woman admitted her mistake and strove diligently to overcome and uproot her jealousy. Later she realised the Dhamma.