Mandukya Karika, verse 3.20

Sanskrit text, IAST transliteration and English translation

अजातस्यैव भावस्य जातिमिच्छन्ति वादिनः ।
अजातो ह्यमृतो भावो मर्त्यतां कथमेष्यति ॥ २० ॥

ajātasyaiva bhāvasya jātimicchanti vādinaḥ |
ajāto hyamṛto bhāvo martyatāṃ kathameṣyati || 20 ||

20. The disputants (i.e., the dualists) contend that the ever-unborn (changeless) entity (Ātman) undergoes a change. How could an entity which is changeless and immortal partake of the nature of the mortal?

Śaṅkara's Commentary

Some interpreters of the Upaniṣads, who¹ are garrulous and who put on the airs of the Knowers of Brahman, admit that the Reality—the Ātman—which is by nature ever-unborn (changeless) and immortal, really passes² into birth (i.e., becomes the universe). If,³ according to them, the Ātman really passes into birth it must undergo destruction. But,⁴ how is it possible for the Ātman which is, by its very nature, ever-unborn (changeless) and immortal to become mortal, i.e., to be subject to destruction? It can never become mortal which is contrary to its very nature.

Anandagiri Tika (glossary)

¹ Who, etc.—i.e., who, in reality, do not know anything about Brahman.

² Passes, etc.—That is, it creates itself into the manifold universe.

³ If, etc.—For, destruction is the inevitable consequence of all objects that are born.

⁴ But, etc.—Birth means change of nature. An entity cannot be changeless while giving birth to other objects. Hence the theory that Ātman somehow changes into the universe is fallacious.