Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.1.4

1.4.1.4

sa vā eti ca preti cānvāha | gāyatrīmevaitadarvācīṃ ca parācīṃ ca yunakti parācyaha devebhyo yajñaṃ vahatyarvācī manuṣyānavati tasmādvā eti ca preti cānvāha

He recites with 'â (hither)!' and 'pra (forth or thither)!' He thereby joins a gâyatrî verse directed hitherward to one directed away from here: the one which tends from hence carries the sacrifice to the gods, and the one which tends hitherward pleases the men. For this reason he recites with 'â' and 'pra.'