Mandukya Karika, verse 1.27


सर्वस्य प्रणवो ह्यादिर्मध्यमन्तस्तथैव च ।
एवं हि प्रणवं ज्ञात्वा व्यश्नुते तदनन्तरम् ॥ २७ ॥

sarvasya praṇavo hyādirmadhyamantastathaiva ca |
evaṃ hi praṇavaṃ jñātvā vyaśnute tadanantaram || 27 ||

27. Aum is verily the beginning, middle and end of all. Knowing Aum as such, one, without doubt, attains immediately to that (the Supreme Reality).

Shankara Bhashya (commentary)

Aum 1 is the beginning, middle and end of all; that is, everything originates from Aum, is sustained by it and ultimately merges in it. As2 the magician, etc. (without undergoing any change in themselves) stand in relation to the illusory elephant, (the illusion of) snake-rope, the mirage and the dream, etc., so also is the sacred syllable Aum to the manifested manifold such as Ākāśa (ether), etc. The meaning is that he who knows thus, the Aum, Ātman, which, like the magician, etc., does not undergo any change, at3 once becomes unified with it.