Bhagavad Gita: Chapter 17, Verse 19

मूढग्राहेणात्मनो यत्पीडया क्रियते तप: |
परस्योत्सादनार्थं वा तत्तामसमुदाहृतम् || 19||

mūḍha-grāheṇātmano yat pīḍayā kriyate tapaḥ
parasyotsādanārthaṁ vā tat tāmasam udāhṛitam

mūḍhathose with confused notions; grāheṇawith endeavor; ātmanaḥone’s own self; yatwhich; pīḍayātorturing; kriyateis performed; tapaḥausterity; parasyaof others; utsādana-arthamfor harming; or; tatthat; tāmasamin the mode of ignorance; udāhṛitamis described to be


BG 17.19: Austerity that is performed by those with confused notions, and which involves torturing the self or harming others, is described to be in the mode of ignorance.


Mūḍha grāheṇāt refers to people with confused notions or ideas, who in the name of austerity, heedlessly torture themselves or even injure others without any respect for the teachings of the scriptures or the limits of the body. Such austerities accomplish nothing positive. They are performed in bodily consciousness and only serve to propagate the grossness of the personality.