Mbh 12.36.1a

"'Vyasa said, "By penances, religious rites, and gifts, O Bharata, a man may wash off his sins if he does not commit them again. By subsisting upon only one meal a day, and that procured by mendicancy, by doing all his acts himself (without relying on the aid of a servant), by making his round of mendicancy with a human skull in one hand and a khattanga in another, by becoming a Brahmacharin and always ready for exertion, by casting off all malice, by sleeping on the bare ground, by publishing his offence to the world, by doing all this for full twelve years, a person can cleanse himself from the sin of having slain a Brahmana. By perishing upon the weapon of a person living by the use of arms, of one's own will and upon the advice of persons learned in the scriptures, or by throwing one's self down, for three times, with head downwards, upon a blazing fire, or by walking a hundred Yojanas all the while reciting the Vedas, or by giving away one's whole property to a Brahmana conversant with the Vedas, or at least so much as would secure to him a competence for life, or a house properly furnished, and by protecting kine and Brahmanas, one may be cleansed of the sin of having slain a Brahmana. By living upon the scantiest meal every day for a space of six years, a person may be cleansed of that sin.[115] By observing a harder vow with regard to food one may be cleansed in three years.[116] By living upon one meal a month, one may be cleansed in course of only a year. By observing, again, an absolute fast, one may be cleansed within a very short time. There is no doubt again that one is cleansed by a Horse-sacrifice. Men that have been guilty of having slain a Brahmana and that have succeeded in taking the final bath at the completion of the Horse-sacrifice, become cleansed of all their sins. This is an injunction of great authority in the Srutis.