Anushasana Parva 140.34

Maheshvara said Listening to the mysteries of religion and duty, observance of the vows laid down in the Vedas, attention to the sacred fire, and accomplishment of the business of the preceptor, leading a mendicant life, always bearing the sacred thread, constant recitation of the Vedas, and rigid observance of the duties of a celebrate life, constitute the duties of the Brahmana.