Khandogya-Upanishad: Second Prapathaka, Eighth Khanda
1. Next for the sevenfold Saman. Let a man meditate on the sevenfold Saman in speech. Whenever there is in speech the syllable hun, that is hinkara, pra is the prastava, a is the adi, the first, i.e. Om,
2. Ud is the udgitha, pra the pratihara, upa the upadrava, ni the nidhana.
3. Speech yields the milk, which is the milk of speech itself, to him who knowing this meditates on the sevenfold Saman in speech. He becomes rich in food, and able to eat food.