Srimad Bhagavatam Canto 06, Chapter 17, Text 39

SB 6.17.39

etat te sarvam akhyatam
 yan mam tvam pariprcchasi
vrtrasyasura-jates ca
 karanam bhagavan-mateh
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
My dear King Pariksit, you inquired from me how Vrtrasura, a great devotee, took birth in a demoniac family. Thus I have tried to explain to you everything about this.
Srimad Bhagavatam Canto 06, Chapter 17, Text 38
Srimad Bhagavatam Canto 06, Chapter 17, Text 40