Mbh 12.268.4b

With clarified butter, milk, curds, dung, curds mixed with milk, skin, the hair in her tail, horns, and hoofs, the cow alone is able to furnish all the necessaries of sacrifice. Particular ones amongst these that are laid down for particular sacrifices, coupled with Ritwijas and presents (to the priests themselves and other Brahmanas) together sustain sacrifices.[1233] By collecting these things together, people accomplish sacrifices[1234]. This Sruti, consistent with the truth, is heard that all things have been created for the performance of sacrifice. It was thus that all men of ancient time set themselves to the performance of sacrifices. As regards that person, however, who performs sacrifices because of the conviction that sacrifices should be performed and not for the sake of fruit or reward, it is seen that he does not injure any creature or bear himself with hostility to anything, or set himself to the accomplishment of any worldly task.[1235] Those things that have been named as the limbs of sacrifice, and those other things that have been mentioned as required in sacrifices and that are indicated in the ordinances, all uphold one another (for the completion of sacrifices) when used according to the approved ritual.[1236] I behold also the Smritis compiled by the Rishis, into which the Vedas have been introduced. Men of learning regard them as authoritative in consequence of their following the Brahmanas.[1237] Sacrifices have the Brahmanas for that progenitor, and truly they rest upon the Brahmanas. The whole universe rests upon sacrifice, and sacrifice rests upon the universe.[1238] The syllable Om is the root from which the Vedas have sprung. (Every rite, therefore, should commence with the utterance of that syllable of vast import).