Mahabharata 12.32.2

12.32.2

prajānāṃ pālanaṃ dharmo rājñāṃ rājīvalocana |
dharmaḥ pramāṇaṃ lokasya nityaṃ dharmānuvartanam || 2 ||

"Vyasa said, 'O thou of eyes like lotus petals, the protection of subjects is the duty of kings. Those men that are always observant of duty regard duty to be all powerful. Do thou, therefore, O king, walk in the steps of thy ancestors. With. Brahmanas, penances are a duty. This is the eternal ordinance of the Vedas. Penances, therefore, O bull of Bharata's race, constitute the eternal duty of Brahmanas. A Kshatriya is the protector of all persons in respect of their duties. That man who, addicted to earthly possessions, transgresses wholesome restraints, that offender against social harmony, should be chastised with a strong hand. That insensate person who seeks to transgress authority, be he an attendant, a son, or even a saint, indeed,--all men of such sinful nature, should by every means be chastised or even killed. That king who conducts himself otherwise incurs sin. He who does not protect morality when it is being disregarded is himself a trespasser against morality. The Kauravas were trespassers against morality. They have, with their followers, been slain by thee. Thou hast been observant of the duties of thy own order. Why then, O son of Pandu, dost thou indulge in such grief? The king should slay those that deserve death, make gifts to persons deserving of charity, and protect his subjects according to the ordinance.'