Khandogya-Upanishad: Sixth Prapathaka, Fifth Khanda
1. “The earth (food) when eaten becomes threefold; its grossest portion becomes feces, its middle portion flesh, its subtilest portion mind.
2. “Water when drunk becomes threefold; its grossest portion becomes water, its middle portion blood, its subtilest portion breath.
3. “Fire (i.e. in oil, butter, &c.) when eaten becomes threefold; its grossest portion becomes bone, its middle portion marrow, its subtilest portion speech.
4. “For truly, my child, mind comes of earth, breath of water, speech of fire.”
“Please, Sir, inform me still more,” said the son.
“Be it so, my child,” the father replied.