Skandapurana 6.3.83.110

6.3.83.110

gandharvāpsaraso nāgāḥ khurāgreṣu vyavasthitāḥ .
pṛthivyāṃ sāgarāntāyāṃ yāni tīrthāni bhārata .
tāni sarvāṇi jānīyādgaurgavyaṃ tena pāvanam .. 83.110 ..

Gandharvas, apsarases, and nāgas reside on the tips of her hooves. / Whatever sacred fords there are on the earth bounded by the oceans, O Bhārata, / one should know all of them [to be in the cow]; therefore cow products are purifying.