The Mandukya Upanishad (Gaudapa Karika and Shankara Bhashya)
Mandukya Karika, verse 4.96
This is verse 4.96 of the Mandukya Karika English translation, including commentaries by Gaudapada (Karika), Shankara (Bhashya) and a glossary by Anandagiri (Tika). Alternate transliteration: Māṇḍūkya-upaniṣad 4.96, Gauḍapāda Kārikā, Śaṅkara Bhāṣya, Ānandagiri Ṭīkā.
Sanskrit text, IAST transliteration and English translation
अजेष्वजमसंक्रान्तं धर्मेषु ज्ञानमिष्यते ।
यतो न क्रमते ज्ञानमसंगं तेन कीर्तितम् ॥ ९६ ॥
ajeṣvajamasaṃkrāntaṃ dharmeṣu jñānamiṣyate |
yato na kramate jñānamasaṃgaṃ tena kīrtitam || 96 ||
96. Knowledge (consciousness), the essence of the Jīvas (who are unborn), is admitted to be itself unborn and unrelated (to any external object). This knowledge is proclaimed to be unconditioned as it is not related to any other object (which, really speaking, does not exist).
Shankara Bhashya (commentary)
What constitutes the highest Wisdom (i.e., the wisdom of the knower of the non-dual Ātman)? This is thus explained: Knowledge which constitutes the essence of the Dhūrmas (Jīvas), unborn, immutable and identical with Ātman, is also admitted to be unborn1 and immutable. It is just like the light and the heat belonging to the sun. Knowledge, being ever unrelated to other2 objects, is said to be unborn. As knowledge is, thus, unrelated to other objects, it is like the Ākāśa, called unconditioned or absolute.
Anandagiri Tika (glossary)
1 Unborn, etc.—This refutes the theory of the Nyāya realists who say that knowledge is an attribute of Ātman and arises only by the contact of the mind with an external object. It has already been pointed out that the appearance of external objects is due to illusion. But consciousness (Ātman) does not cease to exist in the absence of objects as in Yoga Samādhi or deep-sleep. Therefore the real nature of knowledge is that it is unborn and unattached. From the standpoint of Reality the Jīva is identical with consciousness like the identity of the sun with its heat and light.
2 Other objects—It is because such objects do not, from the standpoint of Reality, exist.