Mahabharata Bhishma Parva Chapter 25:3

Mahabharata Bhishma Parva (Bhagavat-Gita Parva) Chapter 25:3 Bhagavad Gita Chapter I Even if these, with judgments perverted by avarice, do not see the evil that ariseth from the extermination of a race, and the sin of internecine quarrels, why should not we, O Janardana, who see the evils of the extermination of a race, learn to abstain from that sin? A race being destroyed, the eternal customs of that race are lost; and upon those customs being lost, sin overpowers the whole race. From the predominance of sin, O Krishna, the women of that race become corrupt. And the women becoming corrupt, an intermingling of castes happeneth, O descendant of Vrishni. This intermingling of castes leadeth to hell both the destroyer of the race and the race itself. The ancestors of those fall (from heaven), their rites of pinda and water ceasing. By these sins of destroyers of races, causing intermixture of castes, the rules of caste and the eternal rites of families become extinct. We have heard, O Janardana, that men whose family rites become extinct, ever dwell in hell. Alas, we have resolved to perpetrate a great sin, for we are ready to slay our own kinsmen from lust of the sweets of sovereignty. Better would it be for me if the sons of Dhritarashtra, weapon in hand, should in battle slay me (myself) unavenging unarmed. Sanjaya continued,—"Having spoken thus on the field of battle, Arjuna, his mind troubled with grief, casting aside his bow and arrows, sat down on his car. Here ends the first lesson entitled "Survey of Forces" in the dialogue between Krishna and Arjuna of the Bhagavadgita, the essence of religion, the knowledge of Brahma, and the system of Yoga, comprised within the Bhishma Parva of the Mahabharata of Vyasa containing one hundred thousand verses.