Bhagavad Gita 17.5

अशास्त्रविहितं घोरं तप्यन्ते ये तपो जनाः।दम्भाहङ्कारसंयुक्ताः कामरागबलान्विताः॥

aśāstravihitaṃ ghoraṃ tapyante ye tapo janāḥ |dambhāhaṅkārasaṃyuktāḥ kāmarāgabalānvitāḥ ||

Those men who practice terrific austerities not prescribed by the scriptures, given to hypocrisy and egoism, driven by the force of lust and attachment.

Those who practice austerities not commanded by scripture, who are enslaved to hypocrisy and egotism, who are carried away by the fury of desire and passion,

Our plain-language meaning of this verse is waiting for scholar review.