Bhagavad Gita 17.19
Austerity done under delusion, and accompanied with sorcery or the infliction of pain upon oneself or another, may be assumed to spring from ignorance.
मूढग्राहेणात्मनो यत्पीडया क्रियते तपः।परस्योत्सादनार्थं वा तत्तामसमुदाहृतम्॥mūḍhagrāheṇātmano yatpīḍayā kriyate tapaḥ|parasyotsādanārthaṃ vā tattāmasamudāhṛtam||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).