Chandogya Upanishad 1.13

ayaṃ vāva loko hāukāraḥ vāyur hāikāraḥ candramā athakāraḥ ātmehakāraḥ agnir īkāraḥ

The syllable Hâu is this world (the earth), the syllable Hâi the air, the syllable Atha the moon, the syllable Iha the self, the syllable Î is Agni, fire.

āditya ūkāraḥ nihava ekāraḥ viśve devā auhoyikāraḥ prajāpatir hiṅkāraḥ prāṇaḥ svaraḥ annaṃ yā vāg virāṭ

The syllable Û is the sun, the syllable E is the Nihava or invocation, the syllable Auhoi is the Visve Devas, the syllable Hin is Pragâpati, Svara (tone) is breath (prâna), the syllable Yâ is food, the syllable Vâg is Virâg.

aniruktas trayodaśaḥ stobhaḥ saṃcaro huṅkāraḥ

The thirteenth stobha syllable, viz. the indistinct syllable Huṅ, is the Undefinable (the Highest Brahman).

dugdhe 'smai vāg dohaṃ yo vāco dohaḥ annavān annādo bhavati ya etām evaṃ sāmnām upaniṣadaṃ vedopaniṣadaṃ veda

Speech yields the milk, which is the milk of speech itself to him who knows this Upanishad (secret doctrine) of the Sâmans in this wise. He becomes rich in food, and able to eat food,—yea, able to eat food.