Śatapatha Brāhmaṇa ("of a hundred paths") 1.1.2.3

1.1.2.3

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

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