Bhagavatapurana 12.6.40

12.6.40

śṛṇoti ya imaṃ sphoṭaṃ supta-śrotre ca śūnya-dṛk /
yena vāg vyajyate yasya vyaktir ākāśa ātmanaḥ //

40. He is Paramatman who hears this sound even when the sense of hearing is closed against external objects and his conscious nature remains the same even when all the senses are suspended and by that sacred syllable is produced the great speech (Vedas), and it is evolved into an audible thing in the space of Atman's heart,