Kauṣītaki Upaniṣad 3.8

3.8

karmakārayati taṃ yamadho ninīṣate eṣa lokapāla eṣa lokādhipatireṣa sarveśaḥsa
ma ātmeti vidyātsa ma ātmeti vidyāt

Let no man try to find out what speech is, let him know the speaker. Let no man try to find out what odour is, let him know him who smells. Let no man try to find out what form is, let him know the seer. Let no man try to find out what sound is, let him know the hearer. Let no man try to find out the tastes of food, let him know the knower of tastes. Let no man try to find out what action is, let him know the agent. Let no man try to find out what pleasure and pain are, let him know the knower of pleasure and pain. Let no man try to find out what happiness, joy, and offspring are, let him know the knower of happiness, joy, and offspring. Let no man try to find out what movement is, let him know the mover. Let no man try to find out what mind is, let him know the thinker. These ten objects (what is spoken, smelled, seen, &c.) have reference to pragñâ (self-consciousness), the ten subjects (speech, the senses, mind) have reference to objects. If there were no objects, there would be no subjects; and if there were no subjects, there would be no objects. For on either side alone nothing could be achieved. But that (the self of pragñâ, consciousness, and prâna, life) is not many, (but one.) For as in a car the circumference of a wheel is placed on the spokes, and the spokes on the nave, thus are these objects (circumference) placed on the subjects (spokes), and the subjects on the prâna. And that prâna (breath, the living and breathing power) indeed is the self of pragñâ (the self-conscious self), blessed, imperishable, immortal. He does not increase by a good action, nor decrease by a bad action. For he (the self of prâna and pragñâ) makes him, whom he wishes to lead up from these worlds, do a good deed; and the same makes him, whom he wishes to lead down from these worlds, do a bad deed. And he is the guardian of the world, he is the king of the world, he is the lord of the universe,--and he is my (Indra's) self, thus let it be known, yea, thus let it be known!

3.8.p1

iti ṛgvedāntargatakauṣītakibrāhmaṇāraṇyakopaniṣatsutṛtīyo'dhyāyaḥ