Taittirīya Upaniṣad 2.6

2.6.1

asanneva sa bhavati /
asadabrahmeti veda cet /
asti brahmeti cedveda /
santamenaṃ tato viduriti /
tasyaiṣa eva śārīra ātmā /
yaḥ pūrvasya /
athāto 'nupraśnāḥ /
utāvidvānamuṃ lokaṃ pretya /
kaścana gacchatī3
āho vidvānamuṃ lokaṃ pretya kaścitsamaśnutā3u /
so 'kāmayata /
bahu syāṃ prajāyeyeti /
sa tapo 'tapyata /
sa tapastaptvā /
idam̐ sarvamasṛjata /
yadidaṃ kiñca /
tatsṛṣṭvā /
tadevānuprāviśat /
tadanupraviśya /
sacca tyaccābhavat /
niruktaṃ cāniruktaṃ ca /
nilayanaṃ cānilayanaṃ ca /
vijñānaṃ cāvijñānaṃ ca /
satyaṃ cānṛtaṃ ca satyamabhavat /
yadidaṃ kiñca /
tatsatyamityācakṣate /
tadapyeṣa śloko bhavati // 1//
iti ṣaṣṭho 'nuvākaḥ //

Non-existent (_a-sat_) himself does one become,
If he knows that Brahma is non-existent.
If one knows that Brahma exists,
Such a one people thereby know as existent.

This, indeed, is its bodily self, as of the former.

Now next, the appurtenant questions (_anu-praśna_):—

Does any one who knows not,
On deceasing, go to yonder world?
Or is it that any one who knows,
On deceasing, attains yonder world?

He desired: ‘Would that I were many! Let me procreate myself!’ He performed austerity. Having performed austerity, he created this whole world, whatever there is here. Having created it, into it, indeed, he entered. Having entered it, he became both the actual (*sat*) and the yon (*tya*), both the defined (*nirukta*) and the undefined, both the based and the non-based, both the conscious (*vijñāna*) and the unconscious, both the real (*satya*) and the false (*anṛta*). As the real, he became whatever there is here. That is what they call the real.

As to that there is also this verse:—