Taittiriyaka-Upanishad: Second Valli, Seventh Anuvaka

“In the beginning this was non-existent (not yet defined by form and name). From it was born what exists. That made itself its Self, therefore it is called the Self-made.” That which is Self-made is a flavour (can be tasted), for only after perceiving a flavour can any one perceive pleasure. Who could breathe, who could breathe forth, if that bliss (Brahman) existed not in the ether (in the heart)? For he alone causes blessedness.

When he finds freedom from fear and rest in that which is invisible, incorporeal, undefined, unsupported, then he has obtained the fearless. For if he makes but the smallest distinction in it, there is fear for him. But that fear exists only for one who thinks himself wise, (not for the true sage.)

On this there is also this Sloka: