SB 7.15.72
aham ca gayams tad-vidvan
stribhih parivrto gatah
jñatva visva-srjas tan me
helanam sepur ojasa
yahi tvam sudratam asu
nasta-srih krta-helanah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Narada Muni continued: Being invited to that festival, I also joined, and, surrounded by women, I began musically singing the glories of the demigods. Because of this, the prajapatis, the great demigods in charge of the affairs of the universe, forcefully cursed me with these words: “Because you have committed an offense, may you immediately become a sudra, devoid of beauty.”
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As far as kirtana is concerned, the sastras say, sravanam kirtanam visnoh: one should chant the glories of the Supreme Lord and the holy name of the Supreme Lord. This is clearly stated. Sravanam kirtanam visnoh: one should chant about and glorify Lord Visnu, not any demigod. Unfortunately, there are foolish persons who invent some process of kirtana on the basis of a demigod’s name. This is an offense. Kirtana means glorifying the Supreme Lord, not any demigod. Sometimes people invent Kali-kirtana or Siva-kirtana, and even big sannyasis in the Mayavada school say that one may chant any name and still get the same result. But here we find that millions and millions of years ago, when Narada Muni was a Gandharva, he neglected the order to glorify the Lord, and being mad in the association of women, he began to chant otherwise. Thus he was cursed to become a sudra. His first offense was that he went to join the sankirtana party in the company of lusty women, and another offense was that he considered ordinary songs, like cinema songs and other such songs, to be equal to sankirtana. For this offense he was punished with becoming a sudra.