Kautilya's Arthashastra 3.1.38

3.1.38

caturvarṇāśramasyāyaṃ lokasyācārarakṣaṇāt /
naśyatāṃ sarvadharmāṇāṃ rājā dharmapravartakaḥ //

In virtue of his power to uphold the observance of the respective duties of the four castes and of the four divisions of religious life, and in virtue of his power to guard against the violation of the Dharmas, the king is the fountain of justice (dharmapravartaka.)