Śatapatha Brāhmaṇa ("of a hundred paths") 1.8.2.17

1.8.2.17

athottamamanuyājamiṣṭvā samānīya juhoti | prayājānuyājā vā ete tadyathaivādaḥ prayājeṣu yajamānāya dviṣantam bhrātṛvyam baliṃ hārayatyattra ādyam baliṃ hārayatyevamevaitadanuyājeṣu baliṃ hārayati

After he has made the last after-offering, he pours together (the butter which remains in the upabhrit with that which attaches to the guhû), and offers it (by pouring it from the guhû in a line from west to east into the fire). For doubtless these are the after-offerings to the fore-offerings: hence even as there, at the fore-offerings, he makes the spiteful enemy pay tribute to the sacrificer, and the one to be consumed pay tribute to the consumer; so now he makes him pay tribute at the after-offerings.