Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.5

2.3.1.5

atha yatprātaranudite juhoti | prajanayatyevainametatso 'yaṃ tejo bhūtvā vibhrājamāna udeti śaśvaddha vai nodiyādyadasminnetāmāhutiṃ na juhuyāttasmādvā etāmāhutiṃ juhoti

And when he offers in the morning before sunrise, then he produces that (sun-child) and, having become a light, it rises shining. But, assuredly, it would not rise, were he not to make that offering: this is why he performs that offering.