Khandogya-Upanishad: Third Prapathaka, Eighth Khanda

2. They enter into that (dark) colour, and they rise from that colour.

3. He who thus knows this nectar, becomes one of the Adityas, with Varuna at their head, he sees the nectar and rejoices. And he, having entered that colour, rises again from that colour.

4. So long as the sun rises in the south and sets in the north, twice as long does it rise in the west and set in the east; and so long does he follow the sovereign supremacy of the Adityas.