Māṇḍūkī Śikṣā 162

162

yeṣāṃ tīrthāgatā vidyā nityamabhyāsavarjitā
te bhavanti durādharṣāḥ saṃsiddhā iva parvatāḥ

Those whose knowledge derived from an authority is constantly devoid of practice, / they become unassailable, like established mountains.