Bhagavad Gita 17.5
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,
अशास्त्रविहितं घोरं तप्यन्ते ये तपो जनाः।दम्भाहङ्कारसंयुक्ताः कामरागबलान्विताः॥aśāstravihitaṃ ghoraṃ tapyante ye tapo janāḥ|dambhāhaṅkārasaṃyuktāḥ kāmarāgabalānvitāḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).