Chandogya Upanishad
annam aśitaṃ tredhā vidhīyate tasya yaḥ sthaviṣṭho dhātus tat purīṣaṃ bhavati yo madhyamas tan māṃsam yo 'ṇiṣṭhas tan manaḥ
'The earth (food) when eaten becomes threefold; its grossest portion becomes feces, its middle portion flesh, its subtilest portion mind.
āpaḥ pītās tredhā vidhīyante tāsāṃ yaḥ sthaviṣṭho dhātus tan mūtraṃ bhavati yo madhyamas tal lohitam yo 'ṇiṣṭhaḥ sa prāṇaḥ
'Water when drunk becomes threefold; its grossest portion becomes water, its middle portion blood, its subtilest portion breath.
tejo 'śitaṃ tredhā vidhīyate tasya yaḥ sthaviṣṭho dhātus tad asthi bhavati yo madhyamaḥ sa majjā yo 'ṇiṣṭhaḥ sā vāk
'Fire (i.e. in oil, butter, &c.) when eaten becomes threefold; its grossest portion becomes bone, its middle portion marrow, its subtilest portion speech.
annamayaṃ hi somya manaḥ āpomayaḥ prāṇaḥ tejomayī vāg iti bhūya eva mā bhagavān vijñāpayatv iti tathā somyeti hovāca
'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.