Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.1.5

1.3.1.5

devā ha vai yajñaṃ tanvānāḥ | te 'surarakṣasebhya āsaṃgādbibhayāṃcakrustadyajñamukhādevaitannāṣṭrā rakṣāṃsyato 'pahanti

For when the gods were performing sacrifice they were afraid of a disturbance on the part of the Asuras and Rakshas. Hence by this means he, from the very opening of the sacrifice, expels from here the evil spirits, the Rakshas.