Mahabharata Anushasna Parva Chapter 126:3

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 126:3 Viswamitra said, 'Listen to a high mystery that is unknown to the generality of men and that is connected with religion. He who offers the Pitris rice boiled in sugared milk, sitting with face directed to the south at noontide in the shade caused by an elephant's body, in the month of Bhadrapada, under the constellation Magha, acquires great merits. Listen to what those merits are. The man who makes such an offering to the Pitris under such circumstances, is regarded as performing a great Sraddha each year for thirteen years in succession.'[] The kine said, 'That man becomes cleansed of all his sins who adores a cow with these Mantras, viz., 'O Vahula, O Samanga, O thou that art fearless everywhere, O thou that art forgiving and full of auspiciousness, O friend, O source of all plenty, in the region of Brahman, in days of yore, thou wert present with thy calf in the sacrifice of Indra, the wielder of the thunderbolt. Thou tookest thy station in the firmament and in the path of Agni. The deities with Narada among them adored thee on that occasion by calling thee Sarvamsaha. Such man attains to the region of Purandara. He acquires, besides, the merits that attach to kine, and the splendour of Chandramas also. Such a man becomes freed from every sin, every fear, every grief. At the end, he obtains residence in the happy region of the Thousand-eyed Indra!'" "'Bhishma continued, "After this, the highly blessed and celebrated seven Rishis, with Vasishtha at their head, rose and circumambulating the Lotus-born Brahman, stood around him with hands joined in reverence. Vasishtha, that foremost of all persons conversant with Brahma, became their spokesman and asked this question that is beneficial to every creature, but especially so to Brahmanas and Kshatriyas, 'By doing what acts may men of righteous conduct who are, however, destitute of the good of this world, succeed in acquiring merits attaching to sacrifices?' Hearing this question of theirs, the Grandsire Brahman began to say what follows. Brahman said, 'Excellent is this question, ye highly blessed ones! It is at once auspicious and high and fraught with a mystery. This question that ye have put is subtil and is fraught with high benefit to mankind. Ye Rishis possessed of wealth of penances, I shall recite everything to you in detail. Do ye listen with attention to what I say as to how men acquire the merits attaching to sacrifices (even when they are unable to perform them through poverty.) In the lighted fortnight of the month of Pausha, when the constellation Rohini is in conjunction, if one, purifying oneself by a bath, lies under the cope of heaven, clad in a single piece of raiment, with faith and concentrated attention, and drinks the rays of the moon, one acquires the merits that attach to the performance of great sacrifices. Ye foremost of regenerate persons, this is a high mystery that I declare unto you in reply to your questions, ye that are possessed of insight into the subtil truths of all topics of enquiry.'