Mahabharata 13.35.7

13.35.7

na śaudraṃ karma kartavyaṃ brāhmaṇena vipaścitā |
śaudraṃ hi kurvataḥ karma dharmaḥ samuparudhyate || 7 ||

"Bhishma said, 'O blessed king, Brahmana, by birth alone, becomes an object of adoration with all creatures and are entitled, as guests, to eat the first portion of all cooked food. From them flow all the great objects of life (viz., Righteousness and Wealth and Pleasure and Emancipation). They are the friends of all creatures in the universe. They are again the mouths of the deities (for food poured into their mouths is eaten by the deities). Worshipped with reverence, they wish us prosperity by uttering words fraught with auspiciousness. Disregarded by our foes, let them be enraged with these, and let them wish evil unto those detractors of theirs, uttering words fraught with severe curses. In this connection, persons conversant with ancient history repeat the following verses sung of old respecting how in ancient times the Creator, after having created the Brahmanas, ordained their duties.--A Brahmana should never do anything else than what has been ordained for him. Protected, they should protect others. By conducting themselves in this way, they are sure to attain to what is mightily advantageous for them. By doing those acts that are ordained for them, they are sure to obtain Brahma-prosperity. Ye shall become the exemplars of all creatures, and reins for restraining them. A Brahmana possessed of learning should never do that which is laid down for the Sudras. By doing such acts, a Brahmana loses merit.