The it that you refer to is a powerful weapon easily misused by the martial artist who deserts his vows.
13 seconds sound clip from the Enter the Dragon (1973) movie soundboard.
You can hear this line at 00:04:00 in the Blu-ray version of the movie.
Quote context
[...]
- A good fight should be... like a small play, but played seriously.
- When the opponent expand, I contract. When he contracts, I expand.
- And when there is an opportunity... I do not hit. It hits all by itself.
- For centuries now, the code of the Shaolin Temple has been preserved.
- Remember, the honor of our brotherhood has been held true.
- Tell me now the Shaolin commandment number 13.
- I'm ashamed to tell you now...
[...]