Ahimsa is one of the five Yamas which forms a pillar of Sanatan Dharmaan is the practice of Non-violence. Patanjali wrote the Yoga Sutras giving the yamas (restraints, or what one should not do) and niyamas (observances, or what one should do). Ahimsa is the first of the yamas. The Yoga Sutras say that once ahimsa is mastered, even wild animals and ferocious criminals will become tame and harmless in our presence.
Ahimsa is closely linked to the law of Karma where every action has an equal reaction, it is an ideal where we practice positivity in our thought, word and actions sending ripples of positive energy into the univers.