Shevi'is chapter 9, mishnah 8. This mishnah describes the mechanics of the mitzvah of bi'ur, and we will explain it according to the approach of the Ramban.
Already in the second mishnah of this chapter we discussed the fact that there are differing opinions as to what bi'ur means:
The Rambam's approach: the fruits must actually be destroyed.
The Ramban's approach: bi'ur means declaring the fruits ownerless - renouncing ownership of them and leaving them available to everyone.
The wording of the mishnah:
"Mi shehayu lo peiros shevi'is v'higia she'as habi'ur" - someone who has shevi'is fruits in his possession, and the time of bi'ur for that type of fruit has arrived. It is worth noting that the beraisa in Maseches Pesachim specifies exact times for the various types of fruit, and all of these times fall in the eighth year, the year following the shemittah year:
Grapes - until Pesach.
Olives - until Shavuos.
Dried figs - until Chanukah.
Dates - until Purim.
When the time arrives for each particular fruit - "mechaleik mazon shalosh se'udos l'chol echad v'echad": he distributes the value of three meals of each type of fruit to every person, including the members of his household, his friends and his acquaintances. The remainder, as the Tosefta puts it, he places at the entrance to his house and announces: "Our brothers, the house of Israel" - whoever needs, let him come and take.
Who eats after bi'ur?
This is the question the mishnah addresses: once the act of bi'ur has been performed and the fruits have been declared ownerless, who may eat from them?
Rabbi Yehudah: "V'he'ani ochel achar habi'ur, aval lo ha'ashirim" - only the poor eat after bi'ur, and not the wealthy.
Rabbi Yosei: "Echad aniyim v'echad ashirim ochlin achar habi'ur" - both the poor and the wealthy eat after the fruits have been declared ownerless.
It should be clarified that 'wealthy' and 'poor' here do not refer to actual wealth: a 'poor person' is anyone who is not the owner of the field, and a 'wealthy person' is the owner of the field. The issue under discussion, then, is whether the owner of the field himself may eat after bi'ur, or only someone who is not the owner of the field. According to Rabbi Yehudah, only someone who is not the owner of the field eats, and the owner cannot acquire the fruits a second time.
The Rambam's approach and the text of the mishnah:
According to the Rambam, who holds that bi'ur means an obligation to destroy the fruits, how is our mishnah to be understood? The Rambam had a different version of the text of the mishnah: according to Rabbi Yosei, neither the poor nor the wealthy eat after bi'ur, since there is an obligation to destroy the fruits. According to the text we have, by contrast, both groups eat after bi'ur.
For this reason our mishnah, as we have it, fits better with the approach of the Ramban, that bi'ur means rendering the fruits ownerless.