Bhagavad Gita 17.19

मूढग्राहेणात्मनो यत्पीडया क्रियते तपः।परस्योत्सादनार्थं वा तत्तामसमुदाहृतम् ॥१७.१९॥

mūḍhagrāheṇātmano yatpīḍayā kriyate tapaḥparasyotsādanārthaṃ vā tattāmasamudāhṛtam

That austerity which is practised out of a foolish notion, with self-torture, or for the purpose of destroying another, is declared to be of the Tamasic nature.

गीता