Mandukya Karika, verse 1.29
अमात्रो'नन्तमात्रश्च द्वैतस्योपशमः शिवः ।
ओंकारो विदितो येन स मुनिर्नेतरो जनः ॥ २९ ॥
amātro'nantamātraśca dvaitasyopaśamaḥ śivaḥ |
oṃkāro vidito yena sa munirnetaro janaḥ || 29 ||
29. One who has known Aum which is soundless and of infinite sounds and which is ever-peaceful on account of negation of duality is the (real) sage and none other.
Shankara Bhashya (commentary)
Amātra 1 or soundless Aum signifies Turīya. Mātrā means “measure”; that which has infinite measure or magnitude is called Anantamātra. That is to say, it is mot possible to determine its extension or measure by pointing to this or that. It is ever-peaceful on account of its being the negation of all duality. He who knows Aum, as explained above, is the (real) sage because he has realised the nature of the Supreme Reality. No2 one else, though he may be an expert in the knowledge of the Scriptures, is a sage.