Khandogya-Upanishad: First Prapathaka, Ninth Khanda
“Ether,” he replied. For all these beings take their rise from the ether, and return into the ether. Ether is older than these, ether is their rest.
2. He is indeed the udgitha (Om = Brahman), greater than great (parovariyas), he is without end. He who knowing this meditates on the udgitha, the greater than great, obtains what is greater than great, he conquers the worlds which are greater than great.
3. Atidhanvan Saunaka, having taught this udgitha to Udara-sandilya, said: “As long as they will know in your family this udgitha, their life in this world will be greater than great.”
4. “And thus also will be their state in the other world.” He who thus knows the udgitha, and meditates on it thus, his life in this world will be greater than great, and also his state in the other world, yea, in the other world.