Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.9

3.9.3.9

tadu haika āhuḥ | devebhyo 'nubrūhīti tadu tathā na brūyāccandāṃsi vai devāḥ prātaryāvāṇaścandāṃsyanuyājā devebhyaḥ preṣya devānyajeti vā anuyājaiścaranti tasmādu brūyāddevebhyaḥ prātaryāvabhyo 'nubrūhītyeva

And so some say, 'Recite to the gods!' But let him not say so; for the early-coming gods are the metres, as the after-offerings are the metres, and the after-offerings are performed with, 'Prompt--to the gods! Recite (the offering-prayer) to the gods!' therefore let him say, 'Recite to the gods, the early-coming!'