Mahabharata Adi Parva Chapter 62:3

Mahabharata Adi Parva Chapter 62:3 He who knoweth this etymology of the name is cleansed of all his sins. And as this history of the Bharata race is so wonderful, that, when recited, it assuredly purifieth mortals from all sins. The sage Krishna-Dwaipayana completed his work in three years. Rising daily and purifying himself and performing his ascetic devotions, he composed this Mahabharata. Therefore, this should be heard by Brahmanas with the formality of a vow. He who reciteth this holy narration composed by Krishna (Vyasa) for the hearing of others, and they who hear it, in whatever state he or they may be, can never be affected by the fruit of deeds, good or bad. The man desirous of acquiring virtue should hear it all. This is equivalent to all histories, and he that heareth it always attaineth to purity of heart. The gratification that one deriveth from attaining to heaven is scarcely equal to that which one deriveth from hearing this holy history. The virtuous man who with reverence heareth it or causeth it to be heard, obtaineth the fruit of the Rajasuya and the horse-sacrifice. The Bharata is said to be as much a mine of gems as the vast Ocean or the great mountain Meru. This history is sacred and excellent, and is equivalent to the Vedas, worthy of being heard, pleasing to the ear, sin-cleansing, and virtue-increasing. O monarch, he that giveth a copy of the Bharata to one that asketh for it doth indeed make a present of the whole earth with her belt of seas. O son of Parikshit, this pleasant narration that giveth virtue and victory I am about to recite in its entirety: listen to it. The sage Krishna-Dwaipayana regularly rising for three years, composed this wonderful history called Mahabharata. O bull amongst the Bharata monarchs, whatever is spoken about virtue, wealth, pleasure, and salvation may be seen elsewhere; but whatever is not contained in this is not to be found anywhere.'"