Mahabharata Anushasna Parva Chapter 125:4

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 125:4 Hence, the Brahmana who is invited to a Sraddha for eating the offerings should eat them after purifying himself by a bath and bear himself piously for that day by abstaining from every kind of injury or evil. The progeny of such a person multiply and he also who feeds him reaps the same reward.'" "'Bhishma continued, "After the Pitris said so, a Rishi of austere penances, named Vidyutprabha, whose form shone with splendour like that of the sun, spoke. Having heard those mysteries of religion as propounded by the Pitris, he addressed Sakra, saying, 'Stupefied by folly, men slay numerous creatures born in the intermediate orders, such as worms and ants and snakes and sheep and deer and birds. Heavy is the measure of sin they incur by these acts. What, however, is the remedy?' When this question was asked, all the gods and Rishis endued with wealth of penances and the highly blessed Pitris, applauded that ascetic. Sakra said, 'Thinking in one's mind of Kurukshetra and Gaya and Ganga and Prabhasa and the lakes of Pushkara, one should dip one's head in water. By so doing one becomes cleansed of all one's sins like Chandramas freed from Rahu. One should bathe in this way for three days in succession and then fast for every day. Besides this, one should touch (after bathing) the back of a cow and bow one's head to her tail.' Vidyutprabha, after this, once more addressing Vasava, said, 'I shall declare a rite that is more subtle. Listen to me, O thou of a hundred sacrifices. Rubbed with the astringent powder of the hanging roots of the banian and anointed with the oil of Priyangu, one should eat the Shashtika paddy mixed with milk. By so doing one becomes cleansed of all one's sins[]. Listen now to another mystery unknown to many but which was discovered by the Rishis with the aid of meditation. I heard it from Vrihaspati while he recited it in the presence of Mahadeva. O chief of the deities, do thou hear it with Rudra in thy company, O lord of Sachi! If a person, ascending a mountain, stands there on one foot, with arms upraised and joined together, and abstaining from food looks at a blazing fire, he acquires the merits of severe penances and obtains the rewards that attach to fasts. Heated by the rays of the sun, he becomes cleansed of all his sins. One who acts in this way in both the summer and the winter seasons, becomes freed from every sin. Cleansed of every sin, one acquires a splendour of complexion for all time. Such a man blazes with energy like the Sun or shines in beauty like the Moon!' After this, the chief of the deities, viz., he of a hundred sacrifices, seated in the midst of the gods, then sweetly addressed Vrihaspati, saying these excellent words, 'O holy one, do thou duly discourse on what those mysteries of religion are that are fraught with happiness to human beings, and what the faults are which they commit, together with the mysteries that attach to them!'