Srimad Bhagavatam Canto 09, Chapter 20, Text 36

SB 9.20.36

antarvatnyam bhratr-patnyam
 maithunaya brhaspatih
pravrtto varito garbham
 saptva viryam upasrjat
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
When the demigod named Brhaspati was attracted by his brother’s wife, Mamata, who at that time was pregnant, he desired to have sexual relations with her. The son within her womb forbade this, but Brhaspati cursed him and forcibly discharged semen into the womb of Mamata.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The sex impulse is so strong in this material world that even Brhaspati, who is supposed to be the priest of the demigods and a very learned scholar, wanted to have a sexual relationship with his brother’s pregnant wife. This can happen even in the society of the higher demigods, so what to speak of human society? The sex impulse is so strong that it can agitate even a learned personality like Brhaspati.
Srimad Bhagavatam Canto 09, Chapter 20, Text 35
Srimad Bhagavatam Canto 09, Chapter 20, Text 37