By oneself the evil is done, by oneself one suffers; by oneself evil is left undone, by oneself one is purified. Purity and impurity belong to oneself, no one can purify another.
from the Dhammapada.
We used to recite this for each training in the martial art I used to practice, although the lines were slightly different:
By doing evil, I contaminate myself. By not doing evil, I purify myself.
