Yajur Veda, Brihadaranyaka Upanishad I, IV-The Creation and Its Cause, 10

 This self was indeed Brahman in the beginning. It knew itself only as I am Brahman. Therefore it became all. And whoever among the gods had this enlightenment, also became That Brahman. It is the same with the seers (rishis), the same with men. The seer Vamadeva, having realized this self as That, came to know: I was Manu and the sun. And to this day, whoever in a like manner knows the self as I am Brahman, becomes all this universe. Even the gods cannot prevent his becoming this, for he has become their Self.