Śrīmad-Bhāgavatam · Text 12.6.37
Who is speaking and story frame
सूत उवाच
समाहितात्मनो ब्रह्मन् ब्रह्मण: परमेष्ठिन: ।
हृद्याकाशादभून्नादो वृत्तिरोधाद् विभाव्यते ॥ ३७ ॥
sūta uvāca
samāhitātmano brahman
brahmaṇaḥ parameṣṭhinaḥ
hṛdy ākāśād abhūn nādo
vṛtti-rodhād vibhāvyate
Sūta Gosvāmī said: O brāhmaṇa, first the subtle vibration of transcendental sound appeared from the sky of the heart of the most elevated Lord Brahmā, whose mind was perfectly fixed in spiritual realization. One can perceive this subtle vibration when one stops all external hearing.
Read the purport on Vedabase.ioFrom Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.