Mbh 12.63.2b

Having studied the Vedas duly and the treatises on the duties of kings, O sinless one, having begotten children and performed other acts of a like nature, having quaffed the Soma and ruled over and protected all his subjects righteously, O foremost of speakers, having performed the Rajasuya, the horse sacrifice, and other great sacrifices, having invited learned Brahmanas for reciting the scriptures and made presents unto them according to their desires, having obtained victories small or great in battle, having placed on his throne the son of his loins or some Kshatriya of good birth for the protection of subjects, having worshipped the Pitris by performing with due rites the sacrifices laid down for honouring them, having attentively worshipped the gods by performing sacrifices and the Rishis by studying the Vedas, the Kshatriya, who in old age desires another mode of life, may, O king, adopt it by leaving that one which immediately precedes it, and by that means he is sure to obtain (ascetic) success. A Kshatriya, for leading the life of a Rishi, O king, may adopt the Bhikshu mode of life; but he should never do so for the sake of enjoying the pleasures of the world. Having left the domestic mode of life, he may adopt the life of mendicancy by begging, what would barely support his life. A life of mendicancy is not obligatory upon the three orders (viz. Kshatriyas, Vaisyas, and Sudras), O giver of profuse presents! Inasmuch, however, as they can adopt it if they choose, this mode of life, therefore, is open to the four orders. Amongst men, the highest duties are those which are practised by Kshatriyas. The whole world is subject to the might of their arms. All the duties, principal and subordinate, of the three other orders, are dependent (for their observance) upon the duties of the Kshatriya. The Vedas have declared this.