Taittirīya Upaniṣad 2.7.1

2.7.1

asadvā idamagra āsīt /
tato vai sadajāyata /
tadātmānam̐ svayamakuruta /
tasmāttatsukṛtamucyata iti /
yadvai tat sukṛtam /
raso vai saḥ /
rasam̐ hyevāyaṃ labdhvā ' 'nandī bhavati /
ko hyevānyātkaḥ
prāṇyāt /
yadeṣa ākāśa ānando na syāt /
eṣa hyevā ' 'nandayāti /
yadā hyevaiṣa etasminnadṛśye 'nātmye 'nirukte 'nilayane 'bhayaṃ
pratiṣṭhāṃ vindate /
atha so 'bhayaṃ gato bhavati /
yadā hyevaiṣa etasminnudaramantaraṃ kurute /
atha tasya bhayaṃ bhavati /
tatveva bhayaṃ viduṣo 'manvānasya /
tadapyeṣa śloko bhavati // 1//
iti saptamo 'nuvākaḥ //

In the beginning, verily, this [world] was non-existent.
Therefrom, verily, Being (*sat*) was produced.
That made itself (*svayam akuruta*) a Soul (Ātman).
Therefore it is called the well-done (*su-kṛta*).

Verily, what that well-done is—that, verily, is the essence (*rasa*) [of existence]. For truly, on getting the essence, one becomes blissful. For who indeed would breathe, who would live, if there were not this bliss in space! For truly, this (essence) causes bliss. For truly, when one finds fearlessness as a foundation in that which is invisible, bodiless (*an-ātmya*), undefined, non-based, then he has reached fearlessness. When, however, one makes a cavity, an interval therein, then he comes to have fear. But that indeed is the fear of one who thinks of himself as a knower.

As to that there is also this verse:—