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

Translation of Bhagavad Gita 17.19

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 Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:    

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 Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

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

Commentary by Sri Ramanuja of Sri Sampradaya:

17.19 Deluded persons are those who lack correct understanding. That austerity which is practised from deluded notion, viz., from the obstinate determination by deluded persons, by self-torture regardless of one’s own capacity or which is performed for causing sufferings to others — that is said to be Tamasika.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Now Lord Krishna explains tapah or austerities that are indicative of tama guna the mode of ignorance. The austerities that consist of foolish concoctions as well as diabolical practices due to an acute lack of discrimination, which is sadistic and masochistic, which causes mental and physical anguish to oneself such as flagellation and causes acute suffering to others such as blood rituals and human and animal sacrifices are irrevocably situated completely in the darkness of tama guna.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Sri Madhvacharya did not comment on this sloka.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

Here Lord Krishna explains that the austerity that is foolishly practiced because of repeated habit and useless attachment or is diabolically engaged in due to depraved perversity where one tortures oneself as in self- mortification to gain power or which causes injury, pain and suffering to other living entities such as blood rituals of animal and human sacrifices, is situated irrevocably in the inertia of darkness in tama guna the mode of ignorance.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

17.19 Yat, that; tapah, austerity; which is kriyate, under-taken; mudha-grahena, with a foolish intent, with a conviction arising out of non-discriminating; pidaya, causing pain; atmanah, to oneself (to one’s body etc.); va, or; utsadanartham, for the destruction; parasya, of another; tat, that; is udahrtam, said to be; an austerity tamasam, born of tamas. Now the classification of charity is being spoken of:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

17.17-19 Sraddhaya etc. upto tamasam udahrtam. There is faith in all the three-fold austerity. the faith of a man of the Sattva is full of austerity itself. The faith of a man of the Rajas is in the Rajas i.e, showing (or hyprocricy) etc. But, the faith (or desire) of a man well established in the Tamas is merely in ruining others. Thus the sage speaks of all the three-fold austerity practised with faith.

Sanskrit Shloka Without Transliteration Marks:

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

Sanskrit to English Word for Word Meanings:

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.