“ When you begin a journey of revenge, start by digging two graves: one for your enemy, and one for yourself. ”
Source: Nineteen Minutes
Additional information: Alternative version "Before you embark on a journey of revenge, dig two graves"- Confucius
Similar Quotes
Be like family to your friends, a friend to strangers, and a stranger to your enemies. 
Treachery and violence are spears pointed at both ends; they wound those who resort to them worse than their enemies. 
The best revenge is not to be like your enemy. 
Never think of pain or danger or enemies a moment longer than is necessary to fight them. 
Never explain- your friends do not need it and your enemies will not believe you anyway. 