Kamasutra 1.5.2

1.5.2

tad viparīta uttamavarṇāsu paraparigṛhītāsu ca/ pratiṣiddho 'varavarṇāsv aniravasitāsu/ veśyāsu punarbhūṣu ca na śiṣṭo na pratiṣiddhaḥ/ sukhārthatvāt//

When Kama is practiced by men of the four castes according to the rules of the Holy Writ (i.e., by lawful marriage) with virgins of their own caste, it then becomes a means of acquiring lawful progeny and good fame, and it is not also opposed to the customs of the world. On the contrary the practice of Kama with women of the higher castes, and with those previously enjoyed by others, even though they be of the same caste, is prohibited. But the practice of Kama with women of the lower castes, with women excommunicated from their own caste, with public women, and with women twice married, is neither enjoined nor prohibited. The object of practicing Kama with such women is pleasure only.