Bhagavad Gita 17.5
अशास्त्रविहितं घोरं तप्यन्ते ये तपो जनाः। दम्भाहङ्कारसंयुक्ताः कामरागबलान्विताः।।17.5।।
aśāstravihitaṃ ghoraṃ tapyante ye tapo janāḥ| dambhāhaṅkārasaṃyuktāḥ kāmarāgabalānvitāḥ||17.5||
ashastravihitam ghoram tapyante ye tapo janah dambhahankarasamyuktah kamaragabalanvitah17.5
Meaning
Those who practice severe austerities not enjoined by the scriptures, driven by hypocrisy and ego, impelled by the force of desire and attachment...
जो लोग शास्त्रविधि से रहित घोर तप करते हैं तथा दम्भ, अहंकार, काम और राग से भी युक्त होते हैं।
This is verse 5 of 28 in Chapter 17 (Shraddhatraya Vibhaga Yoga) of the Bhagavad Gita.