Bhagavatapurana 12.2.8

12.2.8

brahma-viṭ-kṣatra-śūdrāṇāṃ yo balī bhavitā nṛpaḥ /
prajā hi lubdhai rājanyair nirghṛṇair dasyu-dharmabhiḥ //

8. He, who among the four castes—Brahmana, Vaisya, Kshatriya and Sudra, might be the strongest, would become the ruler;