Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.4.13

2.4.4.13

atha yatpūrvedyuḥ | aindrāgnena yajate 'māvāsyāyāṃ tṛtīyasavanamevāsya tadvaiśvadevaṃ vai tṛtīyasavanamindrāgnī vai viśve devāḥ

And again when, at new moon, he offers the Indra-Agni (cake) on the first day, that is for him the same as the third (or evening) libation; for the third libation is sacred to the All-gods, and Indra and Agni truly are all the gods.