Shatapatha Brahmana 10.5.4.2

10.5.4.2

antarikṣaṃ ha tvevaiṣo'gniścitaḥ tasya dyāvāpṛthivyoreva saṃdhiḥ pariśritaḥ pareṇa hāntarikṣaṃ dyāvāpṛthivī saṃdhattastāḥ pariśrito vayāṃsi yajuṣmatya iṣṭakā varṣaṃ sūdadohā marīcayaḥ purīṣamāhutayaḥ samidho vāyurlokampṛṇā tadvā etatsarvaṃ vāyumevābhisampadyate tatsarvo'gnirlo

But, indeed, that Fire-altar also is the air:--the function of heaven and earth (the horizon) is its (circle of) enclosing-stones, for it is beyond the air that heaven and earth meet, and that (junction) is the (circle of) enclosing-stones; the birds are its Yagushmatî bricks, the rain its Sûdadohas, the rays of light its earth-fillings, oblations and fire-logs; Vâyu (the wind) is its space-filler; thus this comes to make up the whole Agni, and the whole Agni comes to be the space-filler; and, verily, whosoever knows this, thus comes to be that whole (Agni) who is the space-filler.