Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.39

2.3.1.39

te hocuḥ | ko na idaṃ hoṣyatīti brāhmaṇa eveti brāhmaṇedaṃ no juhudhīti kim me tato bhaviṣyatītyagnihotrociṣṭameveti sa yatsruci pariśinaṣṭi tadagnihotrociṣṭamatha yatsthālyāṃ yathā parīṇaho nirvapedevaṃ tattasmāttadya eva kaśca pibettadvai nābrāhmaṇaḥ pibedagnau hyadhiśrayanti tasmānnābrāhmaṇaḥ pibet

They then spake, 'Who shall offer this unto us?'--'The priest (brâhmana)!'--'Priest, offer this unto us! What is to be my share then? The residue of the Agnihotra!' Now what he leaves in the ladle, that is the residue of the Agnihotra; and what remains in the pot, is as (the rice for oblations which) one takes out from the enclosed part (of the cart). And if any one is to drink it, at least none but a Brâhman must drink it: for it is put on the fire (and thereby consecrated), and hence none but a Brâhman must drink it.