BG 17.19

मूढग्राहेणात्मनो यत्पीडया क्रियते तपः ।
परस्योत्सादनार्थं वा तत्तामसमुदाहृतम् ॥१९॥

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

mūḍha - foolish; grāheṇa - with endeavor; ātmanaḥ - of one's own self; yat - which; pīḍayā - by torture; kriyate - is performed; tapaḥ - penance; parasya - to others; utsādana-artham - for the sake of causing annihilation; vā - or; tat - that; tāmasam - in the mode of darkness; udāhṛtam - is said to be.

Text

Penance performed out of foolishness, with self-torture or to destroy or injure others, is said to be in the mode of ignorance.

Purport

There are instances of foolish penance undertaken by demons like Hiraṇyakaśipu, who performed austere penances to become immortal and kill the demigods. He prayed to Brahmā for such things, but ultimately he was killed by the Supreme Personality of Godhead. To undergo penances for something which is impossible is certainly in the mode of ignorance.

Bhagavad Gita As It Is.

Chapter 17: The Divisions of Faith. Text 19

Penance performed out of foolishness, with self-torture or to destroy or injure others, is said to be in the mode of ignorance.