Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.32

2.3.1.32

tadvastyeva prajananasyeva rūpam | agnirjyotirjyotiragniḥ svāheti tadubhayato jyotī reto devatayā parigṛhṇātyubhayataḥ parigṛhītaṃ vai retaḥ prajāyate tadubhayata evaitatparigṛhya prajanayati

That (other text), however, has the characteristic form of generation. In saying, 'Agni is the light, the light is Agni, Svâhâ!' he encloses that seed, the light, on both sides with the deity; and the seed, thus enclosed on both sides, is brought forth: thus enclosing it on both sides he causes it to be brought forth.