Srimad-Bhagavatam: Canto 12 - Chapter 1 - Verse 40-41
Sanskrit:
शृणोति य इमं स्फोटं सुप्तश्रोत्रे च शून्यदृक् ।येन वाग् व्यज्यते यस्य व्यक्तिराकाश आत्मन: ॥ ४० ॥स्वधाम्नो ब्राह्मण: साक्षाद् वाचक: परमात्मन: ।स सर्वमन्त्रोपनिषद्वेदबीजं सनातनम् ॥ ४१ ॥
ITRANS:
śṛṇoti ya imaṁ sphoṭaṁsupta-śrotre ca śūnya-dṛkyena vāg vyajyate yasyavyaktir ākāśa ātmanaḥ
Translation:
This oṁkāra, ultimately nonmaterial and imperceptible, is heard by the Supersoul without His possessing material ears or any other material senses. The entire expanse of Vedic sound is elaborated from oṁkāra, which appears from the soul, within the sky of the heart. It is the direct designation of the self-originating Absolute Truth, the Supersoul, and is the secret essence and eternal seed of all Vedic hymns.
Purport:
The senses of a sleeping person do not function until he has awakened. Therefore, when a sleeping person is awakened by a noise, one may ask, “Who heard the noise?” The words supta-śrotre in this verse indicate that the Supreme Lord within the heart hears the sound and awakens the sleeping living entities. The Lord’s sensory activities always function on a superior level. Ultimately, all sounds vibrate within the sky, and in the internal region of the heart there is a type of sky meant for the vibration of Vedic sounds. The seed, or source, of all Vedic sounds is the oṁkāra. This is confirmed by the Vedic statement om ity etad brahmaṇo nediṣṭhaṁ nāma. The full elaboration of the Vedic seed sound is Śrīmad-Bhāgavatam, the greatest Vedic literature.