Srimad Bhagavatam Canto 07, Chapter 07, Text 09

SB 7.7.9

sri-indra uvaca
aste ’sya jathare viryam
 avisahyam sura-dvisah
asyatam yavat prasavam
 moksye ’rtha-padavim gatah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
King Indra said: In the womb of this woman, the wife of the demon Hiranyakasipu, is the seed of that great demon. Therefore, let her remain in our custody until her child is delivered, and then we shall release her.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Indra, the King of heaven, decided to arrest Prahlada Maharaja’s mother because he thought that another demon, another Hiranyakasipu, was within her womb. The best course, he thought, was to kill the child when the child was born, and then the woman could be released.
Srimad Bhagavatam Canto 07, Chapter 07, Text 08
Srimad Bhagavatam Canto 07, Chapter 07, Text 10