Manava Dharmashastra 5.131

5.131

makṣikāgrahaṇaṃ svedajānām | gograhaṇamajailakasya | aśvagrahaṇaṃ hastyaśvatarāṇām | sūryyagrahaṇaṃ jyotiṣāṃ | vipruṣa udabindavaḥ sparśamātrānubhavena yā adṛśyamānarūpaviśeṣāḥ | chāyā caṇḍālādīnām | bhūścaṇḍālādispṛṣṭā padbhyāmākramyamāṇā śuddhā | anyasyāstu saṃmārjanādi vihitam | ete makṣikādayaḥ purīṣādi spṛśanto na dūṣayanti | “ajāśvaṃ mukhato medhyaṃ gāvo medhyā mukhādṛte | mārjāranakulau spṛśyau śubhrāśca mṛgapakṣiṇaḥ ||” iti smṛtyantare |

Another Smṛti-text says—‘Goats and horses are pure in their mouths; cows are pure except in their mouths; cats and mongoose are touchable,—as also other auspicious birds and animals’.—(131).

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