Bhagavad Gita, Chapter 17, Verse 19

मूढग्राहेणात्मनो यत्पीडया क्रियते तपः । परस्योत्सादनार्थं वा तत्तामसमुदाहृतम्

mūḍhagrāheṇātmano yatpīḍayā kriyate tapaḥ | parasyotsādanārthaṃ vā tattāmasamudāhṛtam

Translation

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

— Alladi Mahadeva Sastri

Word meanings

mūḍhagrāheṇa

by foolish, seizing (stubbornness)

ātmanaḥ

of the self

yat

which

pīḍayā

with torture

kriyate

is done

tapaḥ

austerity

parasya

of another

utsādanārtham

of destruction, for the sake

vā

or

tat

that

tāmasam

tāmasic

udāhṛtam

is called

Śaṅkarācārya's commentary

Austerity rooted in delusion, self-torment, or hostile intent toward others falls in the Tāmasic class.