Mahabharata Anushasna Parva Chapter 136:2

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 136:2 The Brahmana who partakes of food at the house of a dead person on the third day after the death, is purified by bathing three times daily for twelve days. After the expiration of twelve days, and going through the purification ceremonies duly, the sin is destroyed by giving clarified butter to Brahmanas. If a man takes any food in the house of a dead person, within ten days after the death, he should go through all the expiations before mentioned, and should recite the Savitri hymn and do the sin-destroying Ishti and Kushmanda penances. The Brahmana who takes his food in the house of a dead person for three nights, becomes purified by performing his ablutions thrice daily for seven days, and thus attains all the objects of his desire, and is never troubled by misfortunes. The Brahmana who takes his food in the company of Sudras is purged from all impurity by duly observing the ceremonies of purification. The Brahmana who takes his food in the company of Vaisyas is absolved from sin by living on alms for three successive nights. If a Brahmana takes his food with Kshatriyas, he should make expiation by bathing with his clothes on. By eating with a Sudra from off the same plate the Sudra loses his family respectability; the Vaisya by eating from off the same plate with a Vaisya, loses his cattle and friends. The Kshatriya loses his prosperity, and the Brahmana his splendour and energy. In such cases, expiations should be made, and propitiatory rites should be observed, and oblations offered to the gods. The Savitri hymn should be recited and the Revati rites and Kushmanda penances should be observed with the view of destroying the sin. If any of the above four classes partake of food partly eaten by a person of any other class, the expiation is undoubtedly made by smearing the body with auspicious substances like Rochana, Durva grass, and turmeric.