Mahabharata Anushasna Parva Chapter 135:2

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 135:2 Professors of the healing art, mercenary soldiers, the priest who acts as warder of the house, and persons who devote a whole year to study without any profit, are all to be considered as Sudras. And those who impudently partake of food offered at ceremonials in a Sudra's house are afflicted with a terrible calamity. In consequence of partaking such forbidden food they lose their family, strength, and energy, and attain to the status of animals, descending to the position of dogs, fallen in virtue and devoid of all religious observances. He who takes food from a physician takes that which is no better than excrement; the food of a harlot is like urine; that of a skilled mechanic is like blood. If a Brahmana approved by the good, takes the food of one who lives by his learning, he is regarded as taking the food of a Sudra. All good men should forego such food. The food of a person who is censured by all is said to be like a draught from a pool of blood. The acceptance of food from a wicked person is considered as reprehensible as the slaying of a Brahmana. One should not accept food if one is slighted and not received with due honours by the giver. A Brahmana, who does so, is soon overtaken by disease, and his race soon becomes extinct. By accepting food from the warder of a city, one descends to the status of the lowest outcaste. If a Brahmana accepts food from one who is guilty of killing either a cow or a Brahmana or from one who has committed adultery with his preceptor's wife or from a drunkard, he helps to promote the race of Rakshasas. By accepting food from a eunuch, or from an ungrateful person, or from one who has misappropriated wealth entrusted to his charge, one is born in the country of the Savaras situated beyond the precincts of the middle country. I have thus duly recited to thee the persons from whom food may be accepted and from whom it may not. Now tell me, O son of Kunti, what else thou wishest to hear from me today.