Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 40
Sanskrit:
गते मयि युवां लब्ध्वा वरं मत्सदृशं सुतम् ।ग्राम्यान् भोगानभुञ्जाथां युवां प्राप्तमनोरथौ ॥ ४० ॥
ITRANS:
gate mayi yuvāṁ labdhvāvaraṁ mat-sadṛśaṁ sutamgrāmyān bhogān abhuñjāthāṁyuvāṁ prāpta-manorathau
Translation:
After you received that benediction and I disappeared, you engaged yourselves in sex to have a son like Me, and I fulfilled your desire.
Purport:
According to the Sanskrit dictionary Amara-kośa, sex life is also called grāmya-dharma, material desire, but in spiritual life this grāmya-dharma, the material desire for sex, is not very much appreciated. If one has a tinge of attachment for the material enjoyments of eating, sleeping, mating and defending, one is not niṣkiñcana. But one really should be niṣkiñcana. Therefore, one should be free from the desire to beget a child like Kṛṣṇa by sexual enjoyment. This is indirectly hinted at in this verse.