Śatapatha Brāhmaṇa ("of a hundred paths") 5.4.4.9

5.4.4.9

sa brahmannityeva prathamamāmantrayate | brahma prathamamabhivyāharāṇi brahmaprasūtāṃ vācaṃ vadānīti tasmādbrahmannityeva prathamamāmantrayate tvam brahmāsītītaraḥ pratyāha savitāsi satyaprasava iti vīryamevāsminnetaddadhāti savitārameva satyaprasavaṃ karoti

'O Brahman!' thus he addresses (the priest) the first time, thinking, 'I will first utter the (word) Brahman, I will speak speech sped by the Brahman:' this is why he first addresses him with 'O Brahman!' The other answers, 'Thou art Brahman! Thou art Savitri of true impulsion!'--he thereby lays vigour into him, and causes Savitri to be of true impulsion.