Text 19

mudha-grahenatmano yat
pidaya kriyate tapah
parasyotsadanartham va
tat tamasam udahrtam

Translation

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

Commentary by Srila Prabhupada 

There are instances of foolish penance undertaken by demons like Hiranyakasipu, who performed austere penances to become immortal and kill the demigods. He prayed to Brahma 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.

Commentary by Sri Visvanatha Cakravarti Thakur

Muda grahena means to be performed out of foolishness. Parasya utsadana artham means performed with the intention of harming others.