Śatapatha Brāhmaṇa ("of a hundred paths") 2.6.1.1

2.6.1.1

mahāhaviṣā ha vai devā vṛtraṃ jaghnuḥ | teno eva vyajayanta yeyameṣāṃ vijitistāmatha yānevaiṣāṃ tasmintsaṃgrāme 'ghnamstānpitṛyajñena samairayanta pitaro vai ta āsaṃstasmātpitṛyajño nāma

Verily, by means of the Great Oblation the gods slew Vritra, and gained that supreme authority which they now wield. And by means of the sacrifice to the fathers they then recalled to life those of them that had been slain in this battle; and they, indeed, were the fathers: hence the name Pitriyagña (sacrifice to the Manes).