Mahabharata Anushasna Parva Chapter 47:5

Mahabharata Anushasna Parva (Dana Dharma Parva) Chapter 32:2 I shall now speak of the sons of a Vaisya by a wife of his own order and by one belonging to the inferior order, as also of the manner in which, O king his wealth is to be distributed among those children. The son born of the Vaisya wife shall take four of such shares of his father's wealth. The fifth share, O Bharata, has been said to belong to the son born of the Sudra wife. Such a son, however, shall take when the father gives. He should not take anything unless the father gives it to him. The son that is begotten on a Sudra wife by persons of the three higher orders should always be regarded as disentitled to any share of the sire's wealth. The Sudra should have only one wife taken from his own order. He can under no circumstances, take any other spouse. Even if he happens to have a century of sons by such a spouse, all of them share equally the wealth that he may leave behind. As regards all the orders, the children born of the spouse taken from the husband's own order shall, it has been laid down, share equally the father's wealth. The eldest son's share shall be greater than that of every other son, for he shall take one share more than each of his brothers, consisting of the best things of his father. Even this is the law of inheritance, O son of Pritha, as declared by the Self-born himself. Amongst children all born of the spouse taken from the husband's own order, there is another distinction, O king! In marrying, the elder ones should always precede the younger ones. The spouses being all equal in respect of their order of birth, and the children also being all equal in respect of the status of their mothers, the son that is first-born shall take one share more than each of his other brothers. The son that comes next in point of age shall take a share that is next in value, while the son that is youngest shall take the share that belongs to the youngest. Thus among spouses of all orders, they that belong to the same order with the husband are regarded as the first. Even this is what was declared by the great Rishi Kasyapa the son of Marichi.