Mbh 12.56.4a

"'"Therefore, do thou observe both kinds of behaviour. O foremost of liberal men, the Brahmanas should never be punished by thee, for the Brahmana, O son of Pandu, is the foremost of beings on the Earth. The high-souled Manu, O king of kings, that sung two Slokas, in respect of thy duties, O thou of Kuru's race, thou shouldst always bear them in mind. Fire hath sprung from water, the Kshatriya from the Brahmana, and iron from stone. The three (viz., fire, Kshatriya and iron) can exert their force on every other thing, but coming into contact with their respective progenitors, their force becomes neutralised. When iron strikes stone, or fire battles with water, or Kshatriya cherishes enmity towards Brahmana, these three soon become weak. When this is so, O monarch, (you will see that) the Brahmanas are worthy of worship. They that are foremost among the Brahmanas are gods on earth. Duly worshipped, they uphold the Vedas and the Sacrifices. But they, O tiger among kings, that desire to have such honour however much they may be impediments to the three worlds, should ever be repressed by the might of thy arms. The great Rishi Usanas, O son, sang two Slokas in days of old. Listen to them, O king, with concentrated attention. The righteous Kshatriya, mindful of his duties, should chastise a Brahmana that may be a very master of the Vedas if he rushes to battle with an uplifted weapon. The Kshatriya, conversant with duties, that upholds righteousness when it is trespassed against, does not, by that act, become a sinner, for the wrath of the assailant justifies the wrath of the chastiser. Subject to these restrictions, O tiger among kings, the Brahmanas should be protected. If they become offenders, they should then be exiled beyond thy dominions. Even when deserving of punishment, thou shouldst, O kings, show them compassion.