SB 6.18.20
sri-rajovaca
katham ta asuram bhavam
apohyautpattikam guro
indrena prapitah satmyam
kim tat sadhu krtam hi taih
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
King Pariksit inquired: My dear lord, due to their birth, the forty-nine Maruts must have been obsessed with a demoniac mentality. Why did Indra, the King of heaven, convert them into demigods? Did they perform any rituals or pious activities?