Mahabharata 13.76.26

13.76.26

imām̐llokānbhariṣyanti haviṣā prasnavena ca |
āsāmaiśvaryamaśnīhi sarvāmṛtamayaṃ śubham || 26 ||

The milk or the froth that escapes from the mouths of calves sucking their dams is never regarded as impure remnant. Chandramas, after drinking the nectar, pours it once more. It is not, however, on that account, looked upon as impure. After the same manner, the milk that these kine yield, being born of nectar, should not be regarded as impure (even though the udders have been touched by the calves with their mouths). The wind can never become impure. Fire can never become impure. Gold can never become impure. The Ocean can never become impure. The Nectar, even when drunk by the deities, can never become impure. Similarly, the milk of a cow, even when her udders are sucked by her calf, can never become impure. These kine will support all these worlds with the milk they will yield and the ghee that will be manufactured therefrom. All creatures wish to enjoy the auspicious wealth, identifiable with nectar, that kine possess!--Having said these words, the lord of creatures, Daksha, made a present unto Mahadeva of a bull with certain kine. Daksha gratified the heart of Rudra, O Bharata, with that present, Mahadeva, thus gratified, made that bull his vehicle. And it was after the form of that bull that Mahadeva adopted the device on the standard floating on his battle-car. For this reason it is that Rudra came to be known as the bull-bannered deity. It was on that occasion also that the celestials, uniting together, made Mahadeva the lord of animals.