Śatapatha Brāhmaṇa ("of a hundred paths") 2.6.2.1

2.6.2.1

mahāhaviṣā ha vai devā vṛtraṃ jaghnuḥ | teno eva vyajayanta yeyameṣāṃ vijitistāmatha yānevaiṣāṃ tasmintsaṃgrāma iṣava ārcaṃstānetaireva śalpānniraharanta tānvyavṛhanta yattryambakairayajanta

Verily, by means of the Great Oblation the gods slew Vritra; by it they gained that supreme authority which they now wield. Now whichever of them were hit by (the Asuras’) arrows in that battle, those same darts they extracted, those they pulled out, by performing the Tryambaka-offerings.