Māndukya 4.04

प्रणवो ह्यपरं ब्रह्म प्रणवस्य परं स्मृतम्। अपूर्वोऽनन्तरोऽबाह्योऽनपरं प्रणवोऽव्ययः ॥४॥

praṇavo hy aparaṃ brahma praṇavasya paraṃ smṛtam। apūrvo'nantaro'bāhyo'naparaṃ praṇavo'vyayaḥ ॥4॥

[प्रणवः (praṇavaḥ) - praṇava; sacred syllable Om; हि (hi) - indeed; अपरम् (aparam) - not other; not different; ब्रह्म (brahma) - Brahman; absolute reality; प्रणवस्य (praṇavasya) - of praṇava; of Om; परम् (param) - supreme; highest; स्मृतम् (smṛtam) - is remembered; is regarded; अपूर्वः (apūrvaḥ) - unprecedented; unique; अनन्तरः (anantaraḥ) - without interior; having no inside; अबाह्यः (abāhyaḥ) - without exterior; having no outside; अनपरम् (anaparam) - without another; having no other; प्रणवः (praṇavaḥ) - praṇava; sacred syllable Om; अव्ययः (avyayaḥ) - imperishable;]

Indeed, Praṇava (the sacred syllable Om) is not different from Brahman; of praṇava, the supreme is remembered. Unprecedented, without interior, without exterior, without another, praṇava is imperishable.