Demai, Chapter 6, Mishnah 10. This Mishnah deals with a righteous convert who has joined the Jewish people and has a non-Jewish brother, and the two of them inherit property from their non-Jewish father. The problem is that among the assets there are items from which it is forbidden to derive any benefit, things a Jew may not make use of, such as objects of idolatry or wine.
The ruling of the Mishnah:
The Mishnah teaches that the Jewish brother may say to his non-Jewish brother:
"Tol atah avodah zarah va'ani ma'os" - the non-Jew takes the idols, and the convert takes the money.
"Tol atah yayin va'ani peiros" - the non-Jew takes the wine, from which benefit is forbidden, and the convert takes the permitted produce.
Why is this ruling different from the previous Mishnah?
In the previous Mishnah we learned that when two Jewish brothers inherit, neither one may tell the other to take one type while he himself takes the other type, because he has a share in all of the property. The reason is that a Jew's inheritance to his sons is mid'oraisa, from the Torah, and therefore to a certain degree the property is viewed as though it is already in the son's possession and control immediately upon the father's death, even before they divided it between them. And since he has a share in each of the types, both in the barley and in the wheat, it turns out that in dividing between the two types he is giving up his own share.
With a convert who inherits from his non-Jewish father, however, from the Torah this is not an inheritance at all, and only the Sages instituted it mid'rabbanan. Therefore the property does not truly belong to him and does not enter his possession, and for that reason he may tell his non-Jewish brother to take the items that are forbidden to him while he takes the rest, since the convert never had genuine ownership of those forbidden items.
"Ve'im mishe'ba'u lirshuso - asur" - "And if it is after they have come into his possession, it is forbidden":
The Mishnah concludes by ruling that if they come to make this division after the convert has already acquired the forbidden items, it is prohibited. Once he has acquired them, they belong to him, and a prohibition against deriving benefit means that he may not receive anything at all in exchange for them. So if he gives his brother the forbidden wine and receives produce from him, he has received the produce in exchange for the wine, and that is forbidden, since he has no permission whatsoever to benefit from the wine.
In summary: This Mishnah teaches that a convert and his non-Jewish brother who inherited from their non-Jewish father may divide the property in such a way that the forbidden items fall to the non-Jew's portion and the permitted items to the convert's portion, because a convert's inheritance from his non-Jewish father is not mid'oraisa but rather an enactment of the Sages, and therefore the forbidden items are not considered to have come into his possession. But if the convert has already acquired the forbidden items, the division is no longer permitted, since receiving payment for them is itself deriving benefit from what is forbidden.