Mahabharata Anushasna Parva Chapter 115:4

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 115:4 It has been said that that religion which has acts for its indications has been ordained for householders, O chief of kings, and not for those men who are desirous of emancipation. Manu himself has said that meat which is sanctified with mantras and properly dedicated, according to the ordinances of the Vedas, in rites performed in honour of the Pitris, is pure. All other meat falls under the class of what is obtained by useless slaughter, and is, therefore, uneatable, and leads to Hell and infamy. One should never eat, O chief of Bharata's race, like a Rakshasa, any meat that has been obtained by means not sanctioned by the ordinance. Indeed, one should never eat flesh obtained from useless slaughter and that has not been sanctified by the ordinance. That man who wishes to avoid calamity of every kind should abstain from the meat of every living creature. It is heard that in the ancient Kalpa, persons, desirous of attaining to regions of merit hereafter, performed sacrifices with seeds, regarding such animals as dedicated by them. Filled with doubts respecting the propriety of eating flesh, the Rishis asked Vasu the ruler of the Chedis for solving them. King Vasu, knowing that flesh is inedible, answered that is was edible, O monarch. From that moment Vasu fell down from the firmament on the earth. After this he once more repeated his opinion, with the result that he had to sink below the earth for it. Desirous of benefiting all men, the high-souled Agastya, by the aid of his penances, dedicated, once for all, all wild animals of the deer species to the deities. Hence, there is no longer any necessity of sanctifying those animals for offering them to the deities and the Pitris. Served with flesh according to the ordinance, the Pitris become gratified. Listen to me, O king of kings, as I tell thee this, O sinless one. There is complete happiness in abstaining from meat, O monarch. He that undergoes severe austerities for a hundred years and he that abstains from meat, are both equal in point of merit. Even this is my opinion, In the lighted fortnight of the month of Karttika in especial, one should abstain from honey and meat. In this, it has been ordained, there is great merit. He who abstains from meat for the four months of the rains acquires the four valued blessings of achievements, longevity, fame and might. He who abstains for the whole month of Karttika from meat of every kind, transcends all kinds of woe and lives in complete happiness. They who abstain from flesh by either months or fortnights at a stretch have the region of Brahma ordained for them in consequence of their abstention from cruelty. Many kings in ancient days, O son of Pritha, who had constituted themselves the souls of all creatures and who were conversant with the truths of all things, viz., Soul and Not-soul, had abstained from flesh either for the whole of the month of Karttika or for the whole of the lighted fortnight in that month.