Muṇḍaka Upaniṣad 2.1.1

2.1.1

tad etat satyam.
yathā sudīptāt pāvakād visphuliṅgāḥ sahasraśaḥ prabhavante sarūpāḥ.
tathākṣarād vividhāḥ somya bhāvāḥ prajāyante tatra caivāpiyanti.

1. This is the truth:— As, from a well-blazing fire, sparks By the thousand issue forth of like form, So from the Imperishable, my friend, beings manifold Are produced, and thither also go.