Revākhaṇḍa ascribed to the Vāyupurāṇa (RKV) 83.110

83.110

gandharvāpsaraso nāgāḥ khurāgreṣu vyavasthitāḥ /
pṛthivyāṃ sāgarāntāyāṃ yāni tīrthāni bhārata /
tāni sarvāṇi jānīyād gaurgavyaṃ tena pāvanam //

Gandharvas, Apsarases, and Nāgas are situated on the tips of the hooves. / Whatever pilgrimage places exist on the earth as far as the ocean, O Bhārata, / all of them are known to be in the cow; therefore, cow products are purifying.