Taittirīya Upaniṣad 1.3.2

1.3.2

vāyuḥ sandhānam /
ityadhilokam /
athādhijautiṣam /
agniḥ pūrvarūpam /
āditya uttararūpam /
āpaḥ sandhiḥ /
vaidyutaḥ sandhānam /
ityadhijyautiṣam /
athādhividyam /
ācāryaḥ pūrvarūpam // 2//

Now, with regard to the luminaries.— Fire is the prior form; the sun, the latter form. Water is their conjunction; lightning, the connection.—Thus with regard to the luminaries.

Now, with regard to the world.— The earth is the prior form; the heaven, the latter form. Space is their conjunction; wind, the connection.—Thus with regard to the world.

Now, with regard to knowledge.— The teacher is the prior form; the pupil, the latter form. Knowledge is their conjunction; instruction, the connection.—Thus with regard to knowledge.