Muṇḍaka Upaniṣad 1.1.6

1.1.6

yat tad adreśyam agrāhyam agotram avarṇam acakṣuḥśrotraṃ tad apāṇipādam.
nityaṃ vibhuṃ sarvagataṃ susūkṣmaṃ tad avyayaṃ yad bhūtayoniṃ paripaśyanti
dhīrāḥ.

'That which cannot be seen, nor seized, which has no family and no caste, no eyes nor ears, no hands nor feet, the eternal, the omnipresent (all-pervading), infinitesimal, that which is imperishable, that it is which the wise regard as the source of all beings.'