Chandogya Upanishad 3.1

The sun is indeed the honey of the Devas. The heaven is the cross-beam (from which) the sky (hangs as) a hive, and the bright vapours are the eggs of the bees.

The eastern rays of the sun are the honey-cells in front. The Rik verses are the bees, the Rig-veda (sacrifice) is the flower, the water (of the sacrificial libations) is the nectar (of the flower).

Those very Rik verses then (as bees) brooded over the Rig-veda sacrifice (the flower); and from it, thus brooded on, sprang as its (nectar) essence, fame, glory of countenance, vigour, strength, and health.

That (essence) flowed forth and went towards the sun. And that forms what we call the red (rohita) light of the rising sun.