Mu

[...] Then, all the useless knowledge you have diligently learned till now is thrown away. As a fruit ripening in season, your internality and externality spontaneously become one. As with a mute man who had had a dream, you know it for sure and yet cannot say it. Indeed your ego-shell suddenly is crushed, you can shake heaven and earth. Just as with getting ahold of a great sword of a general, when you meet Buddha you will kill Buddha. A master of Zen? You will kill him, too. As you stand on the brink of life and death, you are absolutely free. You can enter any world as if it were your own playground. How do you concentrate on this Mu? Pour every ounce of your entire energy into it and do not give up, then a torch of truth will illuminate the entire universe.

Mumon