Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 36

Sanskrit:

अन्तर्वत्‍न्यां भ्रातृपत्‍न्यां मैथुनाय बृहस्पति: ।प्रवृत्तो वारितो गर्भं शप्‍त्वा वीर्यमुपासृजत् ॥ ३६ ॥

ITRANS:

antarvatnyāṁ bhrātṛ-patnyāṁmaithunāya bṛhaspatiḥpravṛtto vārito garbhaṁśaptvā vīryam upāsṛjat

Translation:

When the demigod named Bṛhaspati was attracted by his brother’s wife, Mamatā, who at that time was pregnant, he desired to have sexual relations with her. The son within her womb forbade this, but Bṛhaspati cursed him and forcibly discharged semen into the womb of Mamatā.

Purport:

The sex impulse is so strong in this material world that even Bṛhaspati, 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 Bṛhaspati.