Book of Sith, Pg 78 - Rule of Two, Personal Combat
"I have stated that the Force is venom. Because you are a Sith Lord, you realize the truth in my words. You cannot dilute our power! You must also keep yourself strong, not only in numbers, but in combat. The purest expression of victory is through combat. I will not permit my legacy to become a blurred copy of a copy. These pages contain what you must know if you wish to defeat an enemy with a lightsaber or the Force. Do not rely solely on what your own Master has taught you. Study these arts, drink directly from the source."