The works of Ādi Śaṅkarācārya

Viṣṇusahasranāmastotram

Verse 179

अमात्रोऽनन्तमात्रश्च द्वैतस्योपशमः शिवः ।ओंकारो विदितो येन स मुनिर्नेतरो जनः ॥इति ।'ओं तद्ब्रह्म ।ओं तद्वायुः ।ओं तदात्मा ।ओं तत्स

In plain words

It has no measure, and it has measure without end. It is where duality goes quiet. It is wholly good. Whoever knows Oṃ like that is a sage — no one else is, whatever else they know. So it is said. 'Oṃ: that is Brahman. Oṃ: that is the breath. Oṃ: that is your own self. Oṃ: that is the truth—'

Close to the Sanskrit

Measureless, and of endless measure; the quieting of duality; auspicious — by whom the syllable Oṃ is known thus, he is a sage, not the other sort of person. Thus. 'Oṃ, that is Brahman. Oṃ, that is Vāyu. Oṃ, that is the Self. Oṃ, that is [the truth—]'