Śatapatha Brāhmaṇa ("of a hundred paths") 11.3.1.1

11.3.1.1

vāggha vā etasyāgnihotrasyāgnihotrī mana eva vatsastadidam manaśca vākca samānameva sannāneva tasmātsamānyā rajjvā vatsaṃ ca mātaraṃ cābhidadhati teja eva śraddhā satyamājyam

Verily, the Agnihotrî cow is the speech of the Agnihotra, and her calf is its mind. Now these two, mind and speech, whilst being one and the same, are, as it were, distinct from each other: therefore they tie up the calf and its mother with one and the same rope; and the fire, indeed, is faith, and the ghee truth.