Srimad Bhagavatam Canto 06, Chapter 14, Text 02

SB 6.14.2

devanam suddha-sattvanam
 rsinam camalatmanam
bhaktir mukunda-carane
 na prayenopajayate
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Demigods situated in the mode of goodness and great saints cleansed of the dirt of material enjoyment hardly ever render pure devotional service at the lotus feet of Mukunda. [Therefore how could Vrtrasura have become such a great devotee?]
Srimad Bhagavatam Canto 06, Chapter 14, Text 01
Srimad Bhagavatam Canto 06, Chapter 14, Text 03