Mbh 13.33.2c

He, on the other hand, goes to the wall whom they do not love or like. I tell thee truly, O king, that those foolish persons, without doubt, meet with destruction who calumniate the Brahmanas and utter their dispraise. Skilled in praise and dispraise, and themselves the origin or cause of other people's fame and ignominy the Brahmanas, O king, always become angry with those that seek to injure others. That man whom the Brahmanas praise succeeds in growing in prosperity. That man who is censured and is cast off by the Brahmanas soon meets with discomfiture. It is in consequence of the absence of Brahmanas from among them that the Sakas, the Yavanas, the Kamvojas and other Kshatriya tribes have become fallen and degraded into the status of Sudras. The Dravidas, the Kalingas, the Pulandas, the Usinaras, the Kolisarpas, the Mahishakas and other Kshatriyas, have, in consequence of the absence of Brahmanas from among their midst, become degraded into Sudras. Defeat at their hands is preferable to victory over them, O foremost of victorious persons. One slaying all other living creatures in the world does not incur a sin so heinous as that of slaying a single Brahmana. The great Rishis have said that Brahmanicide is a heinous sin. One should never utter the dispraise or calumny of the Brahmanas. Where the dispraise of Brahmanas is uttered, one should sit with face hanging down or leave that spot (for avoiding both the utterer and his words). That man has not as yet been born in this world or will not take birth here, who has been or will be able to pass his life in happiness after quarrelling with the Brahmanas. One cannot seize the wind with one's hands. One cannot touch the moon with one's hand. One cannot support the Earth on one's arms. After the same manner, O king, one is not able to vanquish the Brahmanas in this world."'"