Śatapatha Brāhmaṇa ("of a hundred paths") 5.2.4.17

5.2.4.17

tadagniṃ samādhāya juhoti | devasya tvā savituḥ prasave 'śvinorbāhubhyām pūṣṇo hastābhyāmupāṃśorvīryeṇa juhomīti yajñamukhaṃ vā upāṃśuryajñamukhenaivaitannāṣṭrā rakṣāṃsi hanti hataṃ rakṣaḥ svāheti tannāṣṭrā rakṣāṃsi hanti

Thereupon making up the fire he offers with (Vâg. S. IX, 38), 'At the impulse of the God Savitri I offer with the arms of the Asvins, with the hands of Pûshan, with the strength of the Upâmsu!' for the Upâmsu (cup of Soma) is the mouth (or opening) of the sacrifice: thus he slays the fiends, the Rakshas, by the mouth of the sacrifice;--'Slain is the Rakshas, hail!' thus he slays the fiends, the Rakshas.