Maitri (Maitrāyaṇīya) Upaniṣad 7.4

7.4

viśve devā anuṣṭubekaviṃśo vairājaḥ śaratsamāno varuṇaḥ sādhyā uttarata udyanti tapanti varṣanti stuvanti punarviśanti antarvivareṇekṣanti antaḥśuddhaḥ pūtaḥ śūnyaḥ śānto'prāṇo nirātmānantaḥ ||

4. The Viśvadevas, the Anushṭubh meter, the Ekaviṁśa hymn, the Vairāja chant, the autumn season, the Samāna breath, Varuṇa, the Sādhya gods, issue forth to the north. They shine, they rain, they praise, they enter again within and peer through an opening.

He is pure within, clean, void, tranquil, breathless, selfless, endless.