Bhagavad Gita · Chapter 17: The Three Kinds of Faith
Bhagavad Gita 17.19
मूढग्राहेणात्मनो यत्पीडया क्रियते तपः ।
परस्योत्सादनार्थं वा तत्तामसमुदाहृतम् ॥
mūḍhagrāheṇātmano yatpīḍayā kriyate tapaḥ | parasyotsādanārthaṃ vā tattāmasamudāhṛtam ||
Austerity that is practised out of deluded stubbornness, by torturing oneself, or in order to ruin someone else, is said to be of inertia.
Modern context
Austerity done out of stubborn foolishness, by tormenting oneself, or to harm someone else, is tamasic. This includes the kind of 'discipline' that is really revenge or obstinacy. Fasting to manipulate others, enduring pain to prove a point, punishing oneself out of misguided guilt: all are named here. True discipline is never aimed at harming anyone, including oneself.