Nedarim, Chapter Five, Mishnah Three
In the previous mishnayoth we learned rulings regarding entering a courtyard for someone who by vow is prohibited from receiving benefit from his neighbor. In this mishnah we learn the rules regarding other types of property: a bath-house, an olive press, a house and a field.
1) If one is forbidden by vow to benefit from his neighbor, and he owns a bath-house or an olive press which is leased to someone in the town, and he has an interest in them, he is forbidden [to make use of them];
a) If [he does] not [have an interest in them], he is permitted.
2) If a man says to his neighbor, Konam, if I enter your house, or [Konam] if I purchase your field, and then [the owner] dies or sells it to another, he is permitted [to enter or buy it];
a) [But if he says] Konam, if I enter this house, or [Konam] if I purchase this field, and [the owner] dies or sells it to another, he is forbidden.
Section one: Shimon is prohibited by vow from receiving benefit from Reuven, who owns a bath-house or an olive press. If Reuven rents the bath-house or olive press to a third party, but still retains an interest in them, for instance he gets a percentage of the profits or he did not rent out the whole thing, then Shimon may not enter them, for they are still partially Reuvens property. However, if he retains no interest, and receives only a fixed sum as rent, then Shimon may enter. In the latter case when Shimon enters, he is entering a third persons property, and it is therefore permitted.
Section two: If Shimon says to Reuven, Konam if I enter your house or Konam if I purchase your field, when Reuven dies or sells the property, Shimon may enter his house or buy his field, because it is no longer Reuvens house or field. However, if he says Konam, if I enter this house, or Konam, if I purchase this field, he may not enter the house or buy the field even when they no longer belong to Reuven. In this case the house and the field itself are prohibited to him, no matter who owns them.