Taittiriya Upanishad 1.5

1.5.1

bhūrbhuvaḥ suvariti vā etāstisro vyāhṛtayaḥ /
tāsāmu ha smaitāṃ caturthīm /
māhācamasyaḥ pravedayate /
maha iti /
tat brahma /
sa ātmā /
aṅgānyanyā devatāḥ /
bhūriti vā ayaṃ lokaḥ /
bhuva ityantarikṣam /
suvarityasau lokaḥ // 1//

Bhūḥ, Bhuvaḥ, Suvaḥ—these three, indeed, are the Vyāhṛtis. Of them Māhācamasya knew a fourth one—Maha by name. It is Brahman; it is the Self. The other gods are the limbs. Bhūḥ, indeed, is this world. Bhuvaḥ is the intermediate space. Suvaḥ is the other world. Maha is the sun; through the sun, indeed, do all the worlds flourish. Bhūḥ, indeed, is the fire. Bhuvaḥ is the air. Suvaḥ is the sun. Maha is the moon; through the moon, indeed, all the luminaries flourish. Bhūḥ, indeed, is the Ṛg-Veda. Bhuvaḥ is the Sāma-Veda. Suvaḥ is the Yajur-Veda.

1.5.2

maha ityādityaḥ /
ādityena vāva sarve loka mahīyante /
bhūriti vā agniḥ /
bhuva iti vāyuḥ /
suvarityādityaḥ /
maha iti candramāḥ /
candramasā vāva
sarvāṇi jyotim̐ṣi mahīyante /
bhūriti vā ṛcaḥ /
bhuva iti sāmāni /
suvariti yajūm̐ṣi // 2//

1.5.3

maha iti brahma /
brahmaṇā vāva sarve vedā mahīyante /
bhūriti vai prāṇaḥ /
bhuva ityapānaḥ /
suvariti vyānaḥ /
maha ityannam /
annena vāva sarve prāṇa mahīyante /
tā vā etāścatasraścaturdha /
catasraścatasro vyāhṛtayaḥ /
tā yo veda /
sa veda brahma /
sarve 'smai devā balimāvahanti // 3//
iti pañcamo 'nuvākaḥ //

Maha is Brahman (i.e. Om), for by Brahman (Om), indeed, are all the Vedas nourished. Bhūḥ, indeed, is prāṇa; Bhuvaḥ is apāna; Suvaḥ is vyāna; Maha is food; for by food, indeed, are all the vital forces nourished. These, then, that are four, are (each) fourfold. The Vyāhṛtis are divided into four groups of four (each). He who knows these knows Brahman. All the gods carry presents to him.