Muṇḍaka Upaniṣad 2.2.1

2.2.1

āviḥ sannihitaṃ guhācaraṃ nāma mahat padam atraitat samarpitam.
ejat prāṇan nimiṣac ca yad etaj jānatha sadasadvareṇyam.
paraṃ vijñānād yad variṣṭhaṃ prajānām.

1. Manifest, [yet] hidden; called 'Moving-in-secret';
The great abode! Therein is placed that
Which moves and breathes and winks.
What that is, know as Being (sad) and Non-being (a-sad),
As the object of desire, higher than understanding,
As what is the best of creatures!