Kaṭha Upaniṣad 2.5

2.5

avidyāyām antare vartamānāḥ svayaṃ dhīrāḥ paṇḍitaṃ manyamānāḥ /
dandramyamāṇāḥ pariyanti mūḍhā andhenaiva nīyamānā yathāndhāḥ //

5. Those abiding in the midst of ignorance,
Self-wise, thinking themselves learned,
Running hither and thither, go around deluded,
Like blind men led by one who is himself blind.