Muṇḍaka Upaniṣad 3.1.8

3.1.8

na cakṣuṣā gṛhyate nāpi vācā nānyair devais tapasā karmaṇā vā.
jñānaprasādena viśuddhasattvas tatas tu taṃ paśyate niṣkalaṃ dhyāyamānaḥ.

8. Not by sight is It grasped, not even by speech,
Not by any other sense-organs (_deva_), austerity, or work.
By the peace of knowledge (_jñāna-prasāda_), one's nature purified—
In that way, however, by meditating, one does behold Him who is without parts.