They who practice severe austerities without following the prescription of the scriptures, who are full of hypocrisy and egotism, who are impelled by the force of desire and attachment, who senselessly torture the elements in their body and also Me who dwells within the body, know these ignorant persons to be of demonic nature.
-- Bhagavad Gita (17.05-06)
See also: non-violence and Their suffering is mine.