Kamasutra 2.9.33

2.9.33

evaṃ hy āhuḥ --- ko hi yoṣitāṃ śīlaṃ śaucam ācāraṃ caritraṃ pratyayaṃ vacanaṃ vā śraddhātum arhati/ nisargād eva hi malinadṛṣṭayo bhavanty etā na parityājyāḥ/ tasmād āsāṃ smṛtita eva śaucam anveṣṭavyam/ evaṃ hy āhuḥ --- vatsaḥ prasravaṇe medhyaḥ śvā mṛgagrahaṇe śuciḥ/ śakuniḥ phalapāte tu strīmukhaṃ ratisaṃgame//

The people of the Shurasena country, on the southern bank of the Jumna do everything without any hesitation, for they say that women being naturally unclean, no one can be certain about their character, their purity, their conduct, their practices, their confidences, or their speech. They are not, however, on this account to be abandoned, because religious law, on the authority of which they are reckoned pure, lays down that the udder of a cow is clean at the time of milking, though the mouth of a cow, and also the mouth of her calf, are considered unclean by the Hindoos. Again a dog is clean when he seizes a deer in hunting, though food touched by a dog is otherwise considered very unclean. A bird is clean when it causes a fruit to fall from a tree by pecking at it, though things eaten by crows and other birds are considered unclean. And the mouth of a woman is clean for kissing and such like things at the time of sexual intercourse. Vatsyayana moreover thinks that in all these things connected with love, everybody should act according to the custom of his country, and his own inclination.