Shatapatha Brahmana 10.4.1.14

10.4.1.14

te yadā stuvate yadānuśaṃsati athāsminnetaṃ vaṣaṭkṛte juhoti vaugiti vā eṣa ṣaḍitīdaṃ ṣaḍvidhamannaṃ kṛtvāsmā apidadhātyātmasammitaṃ yadu vā ātmasammitamannaṃ tadavati tanna hinasti yadbhūyo hinasti tadyatkanīyo na tadavati

And when they chant the hymn, and he (the Hotri) afterwards recites (the sastra), he (the Adhvaryu) offers that (cup of Soma) to him (Agni-Pragâpati) as the Vashat-call is uttered. Now 'vauk' is this (Agni), and 'shat' this sixfold food: having prepared it, he offers it to him as proportionate to his body; for food which is proportionate to the body satisfies, and does not injure it; but when there is too much, it does injure it, and when there is too little, it does not satisfy it.