Śatapatha Brāhmaṇa ("of a hundred paths") 1.7.2.6

1.7.2.6

sa yena devebhya ṛṇaṃ jāyate | tadenāṃstadavadayate yadyajate 'tha yadagnau juhoti tadenāṃstadavadayate tasmādyatkiṃ cāgnau juhvati tadavadānaṃ nāma

And, accordingly, in that he is born as (owing) a debt to the gods, in regard to that he satisfies (ava-day) them by sacrificing; and when he makes offerings in the fire, he thereby satisfies them in regard to that (debt): hence whatever they offer up in the fire, is called avadânam (sacrificial portion).