Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.33

2.3.1.33

atha prātaḥ | sūryo jyotirjyotiḥ sūryaḥ svāheti tadubhayato jyotī reto devatayā parigṛhṇātyubhayataḥparigṛhītaṃ vai retaḥ prajāyate tadubhayata evaitatparigṛhya prajanayati tatprajananasya rūpam

And when, in the morning, he says, 'Sûrya is the light, the light is Sûrya, 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; and this, indeed, is the characteristic form of generation.