Srimad Bhagavatam Canto 03, Chapter 14, Text 11

SB 3.14.11

tad bhavan dahyamanayam
 sa-patninam samrddhibhih
prajavatinam bhadram te
 mayy ayunktam anugraham
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Therefore you should be kind towards me by showing me complete mercy. I desire to have sons, and I am much distressed by seeing the opulence of my co-wives. By performing this act, you will become happy.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
In Bhagavad-gita sexual intercourse for begetting children is accepted as righteous. A person sexually inclined for simple sense gratification, however, is unrighteous. In Diti’s appeal to her husband for sex, it was not exactly that she was afflicted by sex desires, but she desired sons. Since she had no sons, she felt poorer than her co-wives. Therefore Kasyapa was supposed to satisfy his bona fide wife.
Srimad Bhagavatam Canto 03, Chapter 14, Text 10
Srimad Bhagavatam Canto 03, Chapter 14, Text 12