Vaishnava Dharmashastra 23.40

23.40

ajāśvaṃ mukhato medhyaṃ na gaur na narajā malāḥ
panthānaś ca viśudhyanti somasūryāṃśumārutaiḥ //

A goat and a horse are pure, as regards their mouths, but not a cow, nor the impure excretions of a man's body; roads are purified by the rays of the moon and of the sun, and by the winds.