Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.35

2.3.1.35

atha prātaḥ | jyotiḥ sūryaḥ sūryo jyotiḥ svāheti tadbahirdhā jyotī reto devatayā karoti bahirdhā vai retaḥ prajātam bhavati tadenatprajanayati

Then, in the morning, by the text, "The light is Sûrya, Sûrya is the light," he places that seed, the light, outside by means of the deity; and the seed thus brought outside he causes to be born.'