Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.28

3.9.3.28

tadyanmaitrāvaruṇacamasena gṛhṇāti | yatra vai devebhyo yajño 'pākrāmattametaddevāḥ praiṣaireva praiṣamaicanpurorugbhiḥ prārocayannividbhirnyavedayaṃstasmānmaitrāvaruṇacamasena gṛhṇāti

The reason why he takes (water) with the Maitrâvaruna's cup is this. When the sacrifice escaped from the gods, the gods endeavoured to call it up by means of (sacrificial) calls (praisha); by means of the puroruk ('shining before') formulas they pleased it (pra-rokaya), and by the nivids they made (their wishes) known (ni-vid) to it. Therefore he takes (water) with the Maitrâvaruna's cup.