Mahabharata 12.72.26

12.72.26

eṣa eva paro dharmo yadrājā rakṣate prajāḥ |
bhūtānāṃ hi yathā dharme rakṣaṇaṃ ca parā dayā || 26 ||

Protection of the subject is the highest duty of the king, since compassion to all creatures and protecting them from injury has been said to be the highest merit. Persons conversant with duties regard that to be the highest merit of the king, when, engaged in protecting all creatures, the king displays compassion towards them. The sin a king incurs by neglecting for a single day to protect his subjects from fear is such that he does not attain to end of his sufferings (for it) in hell till after a thousand years. The merit a king earns by protecting his subjects righteously for a single day is such that he enjoys its reward in heaven for ten thousand years. All those regions that are acquired by persons leading duly the Garhasthya, the Brahmacharya, and the Vanaprastha modes of life, are soon acquired by a king by only protecting his subjects righteously.