Khandogya-Upanishad: Sixth Prapathaka, Sixth Khanda

2. “In the same manner, my child, the subtile portion of earth (food), when eaten, rises upwards, and becomes mind.

3. “That which is the subtile portion of water, when drunk, rises upwards, and becomes breath.

4. “That which is the subtile portion of fire, when consumed, rises upwards, and becomes speech.

5. “For mind, my child, 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.