Manava Dharmashastra 5.128

5.128

sarvastrīṇāmāsyaṃ śuci paricumbanādau | “striyaśca ratisaṃsarga” iti smṛtyantaram | ratisambandhinīṣveva na mātṛbhaginyādiṣu | atra ucchiṣṭapratiṣedho'yaṃ na mantavyo yoṣitaḥ | satyapi ratisambandhitve “nāśnīyādbhāryayā sārdham” itivacanānna bhujyeteti siddhaṃ caturthādhyāye |
nityagrahaṇāṃnna saṃyogavelāyāmeva, kiṃntarhi tadarthāyāmeva pravṛttau |
śakuniḥ phalapātane | pakṣimātravacane'pi śakuniśabdaḥ kākakaṅkādīnāṃ viḍbhujāṃ neṣyate samācārāt | pātanagrahaṇādvṛkṣasthasya phalasyāyaṃ vidhiḥ |
prasrave duhyamānāyā gorvatsaḥ payaḥprakṣaraṇāthaṃ staneṣu saṃśliṣyate | athavācyate “gāvo medhyā mukhādṛte” iti vacanādaśucitve prāpte tannivṛttyarthaṃ vacanamatastadīyāsyasaṃsarśasya | na tu śvā śuciḥ | mṛgaṃ tu yadā''kheṭakādau gṛhṇāti hantuṃ tadā śuciḥ |

The flies &c. mentioned here, even though coming into contact with ordure and other unclean things, do net become sources of defilement.