Khandogya-Upanishad: Second Prapathaka, Eleventh Khanda
1. The hinkara is mind, the prastava speech, the udgitha sight, the pratihara hearing, the nidhana breath. That is the Gayatra Saman, as interwoven in the (five) prânas.
2. He who thus knows this Gayatra interwoven in the prânas, keeps his senses, reaches the full life, he lives long, becomes great with children and cattle, great by fame. The rule of him who thus meditates on the Gayatra is, “Be not high-minded.”