Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.12

2.3.1.12

atha yatprātaranudite juhoti | asya rasasya jīvanasya devebhyo juhavāni yadeṣāmidaṃ sadupajīvāma iti sa yattato 'hnāśnāti hutociṣṭameva tanniravattabalyaśnāti hutociṣṭasya hyevāgnihotraṃ juhvadaśitā

And when he offers in the morning before sunrise, he does so thinking, 'I will offer to the gods of this life-giving juice: we subsist on this which belongs to them.' And when he afterwards takes his meal in the day-time, he eats what remains of the offering, and whereof oblative portions have been distributed all round; for he who performs the Agnihotra eats only what remains of the offering.