Aitareya Upanishad 1.3.13

1.3.13

sa jāto bhūtāny abhivyaikhyat kim ihānyaṃ vāvadiṣad iti.
sa etam eva puruṣaṃ brahmatatamam apaśyad idam adarśam itī3.

Being born, He manifested all the beings;footnote{He knew and spoke distinctly of them as identified with Himself thus: "I am a man", "I am blind", "I am happy", etc.} for did He speak of (or know) anything else?footnote{That is to say, He neither perceived, nor spoke of anyone besides Himself. As He did not perceive any difference, He identified Himself with the individual soul.} He realised this very Puruṣa as Brahman, the most pervasive, thus: “I have realised this.”