Mbh 12.78.8a

"'Bhishma said, "By penances, by Brahmacharya, by weapons, and by (physical) might, applied with or without the aid of deceit, the Kshatriyas should be subjugated. If the Kshatriya misconducts himself, especially towards Brahmanas, the Vedas themselves will subjugate them. The Kshatriyas have sprung from the Brahmanas. Fire has sprung from water; the Kshatriya from the Brahmana; and iron from stone. The energy of fire, the Kshatriya, and iron, are irresistible. But when these come into contact with the sources of their origin, their force becomes neutralised. When iron strikes stone, or fire battles with water, or the Kshatriya becomes hostile to the Brahmana, then the strength of each of those three becomes destroyed. Thus, O Yudhishthira, the energy and might, howsoever great and irresistible, of Kshatriyas become quelled as soon as they are directed against the Brahmanas. When the energy of the Brahmanas becomes mild, when Kshatriya energy becomes weak, when all men misbehave themselves towards the Brahmanas, they that engage in battle then, casting off all fear of death, for protecting the Brahmanas, morality, and their own selves,--those persons, moved by righteous indignation and possessed of great strength of mind, succeed in winning high regions of bliss hereafter. All persons should take up arms for the sake of Brahmanas. Those brave persons that fight for Brahmanas attain to those felicitous regions in heaven that are reserved for persons that have always studied the Vedas with attention, that have performed the austerest of penances, and that have, after fasting, cast off their bodies into blazing fires. The Brahmana, by taking up arms for the three orders, does not incur sin. People say that there is no higher duty than casting off life under such circumstances. I bow to them and blessed be they that thus lay down their lives in seeking to chastise the enemies of Brahmanas. Let us attain to that region which is intended for them.