Mbh 12.188.3a

"'"Bhrigu said, 'There is really no distinction between the different orders. The whole world at first consisted of Brahmanas. Created (equal) by Brahman, men have, in consequence of their acts, become distributed into different orders. They that became fond of indulging in desire and enjoying pleasures, possessed of the attributes of severity and wrath, endued with courage, and unmindful of the duties of piety and worship,--these Brahmanas possessing the attribute of Passion,--became Kshatriyas. Those Brahmanas again who, without attending to the duties laid down for them, became possessed of both the attributes of Goodness and Passion, and took to the professions of cattle-rearing and agriculture, became Vaisyas. Those Brahmanas again that became fond of untruth and injuring other creatures, possessed of cupidity,--engaged in all kinds of acts for a living, and fallen away from purity of behaviour, and thus wedded to the attribute of Darkness, became Sudras. Separated by these occupations, Brahmanas, falling away from their own order, became members of the other three orders. All the four orders, therefore, have always the right to the performance of all pious duties and of sacrifices. Even thus were the four orders at first created equal by Brahman who ordained for all of them (the observances disclosed in) the words of Brahma (in the Vedas). Through cupidity alone, many fell away, and became possessed by ignorance. The Brahmanas are always devoted to the scriptures on Brahma; and mindful of vows and restraints, are capable of grasping the conception of Brahma. Their penances therefore, never go for nothing. They amongst them are not Brahmanas that are incapable of understanding that every created thing is Supreme Brahma. These, falling away, became members of diverse (inferior) orders.