Mbh 12.33.6b

The rejection of one's own creed, the practice of other people's creed, assisting at the sacrifice or the religious rites of one that is not worthy of such assistance, eating of food that is forbidden, deserting one that craves protection, neglect in maintaining servants and dependants, selling salt and treacle (and similar other substances), killing of birds and animals, refusal, though competent, to procreate upon a soliciting woman, omission to present the daily gifts (of handfuls of grass to kine and the like), omission to present the dakshina, humiliating a Brahmana,--these all have been pronounced by persons conversant with duty to be acts that no one should do. The son that quarrels with the father, the person that violates the bed of his preceptor, one that neglects to produce offspring in one's wedded wife, are all sinful, O tiger among men! I have now declared to thee, in brief as also in detail, those acts and omissions by which a man becomes liable to perform expiation. Listen now to the circumstances under which men, by even committing these acts, do not become stained with sin. If a Brahmana well acquainted with the Vedas takes up arms and rushes against thee in battle for killing thee, thou mayst proceed against him for taking his life. By such an act the slayer does not become guilty of the slaughter of a Brahmana.[113] There is a mantra in the Vedas, O son of Kunti, that lays this down, I declare unto thee only those practices that are sanctioned by the authority of the Vedas. One who slays a Brahmana that has fallen away from his own duties and that advances, weapon in hand, with intent to slaughter, does not truly become the slayer of a Brahmana. In such a case it is the wrath of the slayer that proceeds against the wrath of the slain. A person by drinking alcoholic stimulants in ignorance or upon the advice of a virtuous physician when his life is at peril, should have the regenerating ceremonies performed once more in his case.