Bhagavad Gita, Chapter 17, Verse 5

अशास्त्रविहितं घोरं तप्यन्ते ये तपो जनाः । दम्भाहङ्कारसंयुक्ताः कामरागबलान्विताः

aśāstravihitaṃ ghoraṃ tapyante ye tapo janāḥ | dambhāhaṅkārasaṃyuktāḥ kāmarāgabalānvitāḥ

Translation

Those men who practise terrific austerities not enjoined by the scripture, given to hypocrisy and egotism, endued with the strength of lust and passion;

— Alladi Mahadeva Sastri

Word meanings

aśāstravihitam
not, by the Shāstras, ordained
ghoram
terrible
tapyante
endure
ye
who
tapaḥ
austerity
janāḥ
people
dambhāhaṅkārasaṃyuktāḥ
with vanity, and, with egoism, and, joined
kāmarāgabalānvitāḥ
of desire, and, of passion, and, by force, filled

Śaṅkarācārya's commentary

"Terrific": causing pain to himself and to other living beings. "Endued with the strength of lust and passion" may also be interpreted as 'possessed of lust, passion and strength.'