Khandogya-Upanishad: First Prapathaka, Thirteenth Khanda
1. The syllable Hau is this world (the earth), the syllable Hai the air, the syllable Atha the moon, the syllable Iha the self, the syllable I is Agni, fire.
2. The syllable U 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 Ya is food, the syllable Vag is Virâg.
3. The thirteenth stobha syllable, viz. the indistinct syllable Hun, is the Undefinable (the Highest Brahman).
4. Speech yields the milk, which is the milk of speech itself to him who knows this Upanishad (secret doctrine) of the Samans in this wise. He becomes rich in food, and able to eat food,—yea, able to eat food.