Bhagavad Gita · 3.32

ये त्वेतदभ्यसूयन्तो नानुतिष्ठन्ति मे मतम्।सर्वज्ञानविमूढांस्तान्विद्धि नष्टानचेतसः॥

ye tv etad abhyasūyanto nānutiṣhṭhanti me matam sarva-jñāna-vimūḍhāṁs tān viddhi naṣhṭān achetasaḥ

But those who find fault with this teaching and do not follow it — know them to be deluded in all knowledge, ruined and without discrimination.

— Bhagavad Gita 3.32

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)