Mandukya Upanishad, verse 6

एष सर्वेश्वरः एष सर्वज्ञ एषोऽन्तर्याम्येष योनिः सर्वस्य प्रभवाप्ययौ हि भूतानाम् ॥ ६ ॥

eṣa sarveśvaraḥ eṣa sarvajña eṣo'ntaryāmyeṣa yoniḥ sarvasya prabhavāpyayau hi bhūtānām || 6 ||

6. This is the Lord of all; this is the knower of all; this is the controller within; this is the source of all; and this is that from which all things originate and in which they finally disappear.

Shankara Bhashya (commentary)

This in its natural¹ state, is the Lord (Īśvara) of all. All, that is to say, of the entire physical and super-physical universe. He (Īśvara) is not something separate from the universe as others² hold. The Śruti also says, “O good one, Prāṇa (Prājña or Īśvara) is that in which the mind is bound.” He is omniscient because he is the knower³ of all beings in their different conditions. He is the Antaryāmin, that is, he alone entering into all, directs everything from within. Therefore He is called the origin of all because from Him proceeds the universe characterized by diversity, as described before. It being so, He is verily that from which all things proceed and in which all disappear.

Anandagiri Tika (glossary)

¹ Natural state—Prājña is the natural state because in deep sleep all diversities of waking and dream states merge. This state, being free from the conditions of the waking and dream states, manifests, in a marked degree Pure Consciousness.

² Others—The Naiyāvikās and others admit an extra-cosmic creator. Śaṅkara has refuted this theory in the commentary on; the Vedānta Sūtra (2-2-37). When seeking for the cause of the universe, Vedānta posits Prājña as the material as well as the efficient cause of the universe.

³ Knower—The Ātman is the witness of the past, the present and the future as well as the three states. Knowledge of the three states implies the common knower of all.