Mbh 13.77.6c

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. Indeed, the great Rudra became the Master of kine and is named as the bull-signed deity. Hence, O king, in the matter of giving away kine, the gift is regarded as primarily desirable of Kapila kine which are endued with great energy and possessed of colour unchanged (from white). Thus are kine, the foremost of all creatures in the world. It is from them that the means have flowed of the sustenance of all the worlds. They have Rudra for their master. They yield Soma (nectar) in the form of milk. They are auspicious and sacred, and grantors of every wish and givers of life. A person by making a gift of a cow come to be regarded as making a gift of every article that is desired to be enjoyed by men. That man who, desiring to attain to prosperity, reads with a pure heart and body these verses on the origin of kine, becomes cleansed of all his sins and attains to prosperity and children and wealth and animals. He who makes a gift of a cow, O king, always succeeds in acquiring the merits that attach to gifts of Havya and Kavya, to the offer of oblations of water unto the Pitris, to other religious acts whose performance brings peace and happiness, to the gift of vehicles and cloths, and to the cherishing of children and the old."'