Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 1.4.6

1.4.6

athetyabhyamanthatsa mukhācca yonerhastābhyāṃ cāgnimasṛjata tasmādetadubhayamalomakamantarato'lomakā hi yonirantarataḥ | tadyadidamāhuramuṃ yajāmuṃ yajetyekaikaṃ devametasyaiva sā visṛṣṭireṣa u hyeva sarve devāḥ | atha yatkiṃcedamārdraṃ tadretaso'sṛjata tadu soma etāvadvā idam̐ sarvamannaṃ caivānnādaśca soma evānnamagnirannādaḥ saiṣā brahmaṇo'tisṛṣṭiryacchreyaso devānasṛjatātha yanmartyaḥ sannamṛtānasṛjata tasmādatisṛṣṭiratisṛṣṭyām̐ hāsyaitasyāṃ bhavati ya evaṃ veda

Next he thus produced fire by rubbing. From the mouth, as from the fire-hole, and from the hands he created fire. Therefore both the mouth and the hands are inside without hair, for the fire-hole is inside without hair.
And when they say, 'Sacrifice to this or sacrifice to that god,' each god is but his manifestation, for he is all gods.
Now, whatever there is moist, that he created from seed; this is Soma. So far verily is this universe either food or eater. Soma indeed is food, Agni eater. This is the highest creation of Brahman, when he created the gods from his better part, and when he, who was (then) mortal, created the immortals. Therefore it was the highest creation. And he who knows this, lives in this his highest creation.