Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.2.11

2.4.2.11

sa udvāsyāgnau dve āhutī juhoti devebhyaḥ | devānvā eṣa upāvartate ya āhitāgnirbhavati yo darśapūrṇamāsābhyāṃ yajate 'thaitatpitṛyajñenevācārīttadu nihnute sa devaiḥ prasūto 'thaitatpitṛbhyo dadāti tasmādudvāsyāgnau dve āhutī juhoti devebhyaḥ

After removing it (from the fire) he offers to the gods two libations in the fire. For, in establishing his sacrificial fires, and in performing the new and full-moon sacrifice, that (householder) resorts to the gods. Here, however, he is engaged in a sacrifice to the fathers: hence he thereby propitiates the gods, and being permitted by the gods, he presents that (food) to the fathers. This is why, on removing (the rice), he offers to the gods two libations in the fire.