Srimad Bhagavatam Canto 07, Chapter 04, Text 24

SB 7.4.24

tesam avirabhud vani
 arupa megha-nihsvana
sannadayanti kakubhah
 sadhunam abhayankari
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Then there appeared before them a transcendental sound vibration, emanating from a personality not visible to material eyes. The voice was as grave as the sound of a cloud, and it was very encouraging, driving away all fear.
Srimad Bhagavatam Canto 07, Chapter 04, Text 22-23
Srimad Bhagavatam Canto 07, Chapter 04, Text 25-26