Gemara

(Abaye): A Kesuvah is considered to be collected in the lifetime of the Yavam.

Question (Rava - Beraisa - R. Aba): If a Yavam Kohen wants to sell property he inherited from his brother through Yibum, he should appease his wife so she will agree. If he is a Yisrael, he can divorce her and remarry her.

If the Kesuvah is considered collected in his lifetime, he could designate an amount sufficient to pay the Kesuvah and sell the rest!

Counter-question (Abaye - Mishnah): A Yavam, or any man, should not tell his wife 'Your Kesuvah is on the table'. Rather, there is a lien on all his property to pay the Kesuvah.

Answer to both questions: Surely a married man can sell his property! Rather, this is just advice. Also regarding the Yavam, it is just advice.

The question remains (if he could designate enough for the Kesuvah, surely this is better than divorcing her)!

Answer: R. Aba gives a better counsel, to avoid resentment. (Designating money for the Kesuvah makes it looks like he plans to divorce her. If he divorces and remarries her, she realizes that this was only to be able to use the money.)

A woman fell to Yibum. Levi planned to give her a Get, to prevent his older brother Reuven from doing Yibum.

Reuven: Do you do so to prevent me from inheriting our brother's property myself? I will split it with you!

(Rav Yosef): Since Chachamim said that the property may not be sold, Reuven's sale (or gift) is void.

(Beraisa): If a woman fell to Yibum, even if the Mes left 10,000 Zuz and the Kesuvah is only 100 Zuz, there is a lien on all the property. The Yavam may not sell any of it.

Question (Abaye): Sometimes Chachamim forbade selling, but b'Di'eved the sale is valid!

(Mishnah - Beis Shamai): (If property fell to an Arusah,) she may sell it;

Beis Hillel say, she may not sell it.

They agree that if she sold or gave it, the sale or gift stands.

R. Chanina bar Papi agreed with Rav Yosef. Rav Minyomi brei d'Rav Nechumi agreed with Abaye.

Support (Rav Yosef for himself - Beraisa): Reuven owed money to his brother Levi. Levi died and his wife fell to Yibum. Reuven cannot say 'since I inherit, the money will stay by me.' Rather, we take the money from him, buy land with it, and he eats the Peros.

Objection (Rav Minyomi citing Rav Nachman): This Beraisa is erroneous, for no Tana makes two stringencies to enable collecting a Kesuvah:

We find only R. Meir (who says that it may be collected from Metaltelim) or R. Nasan (who says that it may be collected from one who owes the husband).

Another case occurred in which a younger brother wanted to prevent his older brother from doing Yibum. The elder offered to divide the property now to dispel his brother's fear.

(Mar bar Rav Ashi): Here, the division is void. This is unlike R. Yochanan's law:

(Rav Dimi citing R. Yochanan): If Reuven told Shimon 'do Meshichah on this cow, but it is not yours until 30 days from now', 30 days from now he acquires it, even if it is in a swamp (where Meshichah does not work)!

There, Reuven could give the cow now. Here, the Yavam cannot give the property now.

(Ula and Ravin): Whether he divided the property before or after doing Yibum, the division is void.

This is the Halachah.

82b (Mishnah): If he divorces her, she collects only her Kesuvah (and he may sell the rest of the property).

This is only after he divorces her, (but before this he may not sell any property, lest it be needed to pay her Kesuvah,) like R. Aba taught (81a).

Rishonim

Rif and Rosh (Kesuvos 39b and 8:13): A Yavam who planned to do Yibum offered to split the Mes' property with his younger brother. Rav Yosef ruled that since Chachamim forbade selling the property, the gift is void. A Beraisa teaches that if a woman fell to Yibum, even if the Mes left 10,000 Zuz and the Kesuvah is only 100, there is a lien on all the property and the Yavam may not sell any of it. Ravin taught that whether he divided the property before or after doing Yibum, the division is void. This is the Halachah.

Ran (DH ha'Hu): Rashi says that the Yavam's offer is like a sale, and it is invalid. This is difficult, for this does not depend on Rav Yosef's law. The Yavam did not yet inherit the property, therefore he cannot give it! It seems that there were no other brothers, and the elder stipulated not to inherit extra due to Yibum. Such a Tnai works.

Ran (DH v'Hilchesa): If property was designated for a Kesuvah and the property was flooded, she collects from other property, even if there is nothing left except for sold property. Nevertheless the husband may not sell, because she does not want the toil of going to Beis Din to take land from buyers. A Mishnah (Gitin 55b) says that if one bought land from a man and then bought it from his wife, the latter sale is void. This refers to one of three fields special for her Kesuvah: that he wrote in the Kesuvah that she will receive it, that he designated for collection of the Kesuvah, and a field she brought into the marriage.

Rif and Rosh (ibid.): If a Yavam Kohen wants to sell property he inherited from his brother, he should appease his wife so she will agree. If he is a Yisrael, he can divorce her and remarry her.

Rosh (ibid.): Rashi explains that after divorcing her he pays her Kesuvah, sells what he wants and remarries her on condition that the is her initial Kesuvah. Or, he may remarry her before selling. Only a Yavam may not sell, since he did not write to her a Kesuvah with a lien on whatever he will acquire. If he writes this when he remarries her, she cannot stop him from selling.

Hagahos Ashri: Even if he sells fields designated for her Kesuvah, the sale is valid until she takes them away to collect her Kesuvah (if her ex-husband does not have unsold property at the time).

Question: The Mishnah says that if he remarries her, she has no Kesuvah, i.e. from the Yavam himself, rather from the Mes. This is like before divorcing her!

Answer (Rosh): This is when he remarries her Stam. Rashi discusses when he explicitly says that she may collect from what he will acquire. A Tosefta supports this. She would not have agreed to this had he not divorced her.

Rambam (Hilchos Ishus 22:11): The Kesuvah of a Yevamah is collected from the property of the deceased. Therefore, the Yavam may not sell any property of his brother before or after Yibum. If he sold or gave a gift or divided the Mes' property with his brothers, whether before or after Yibum, it is void. This is because the property was already allocated to the widow to collect her Kesuvah from it.

Tosfos (81b DH Ela): Rashi says that one should not tell one's wife that her Kesuvah is on the table, lest he spend it and need to write a new Kesuvah. This is only according to R. Meir. The Ri says that the concern is lest he be quick to divorce her. The Rashba says that regarding a wife we thought that it is because he forbids himself to spend his Metaltelim. We conclude that the concern is enmity, both regarding a Yevamah and a regular wife.

Poskim

Shulchan Aruch (EH 168:3): A Yevamah collects her Kesuvah from the Mes' property. Therefore, the Yavam may not sell any property of his brother. If he sold or gave a gift or divided the Mes' property with his brothers, whether before or after Yibum, it is void.

Beis Yosef (DH v'Chosvu and DH v'Chosav ha'Rashba): Tosfos (Kesuvos 81a DH ha'Rotzeh) says that since the Yevamah did not write a lien on his property to pay her Kesuvah, he cannot sell at all, lest she need to toil in Beis Din to take from buyers. The Rashba says that he cannot even use the property because she cannot make him pay the Kesuvah now, and even after Yibum she has no lien on his property.

Beis Shmuel (3): Tosfos (81b DH Megarshah) says that even if he wants to write to her a Kesuvah on his property (to enable him to sell the Mes' property), she can refuse. Even though the enactment(that the Kesuvah is paid only from the Mes' property) was for his benefit, since he did not decline the enactment at the beginning (when he did Yibum), he cannot decline it now. It seems that if he wanted to decline when he did Yibum, or even before, he can. However, the episode with the Yavam who offered to divide with his brother connotes that he cannot. Also, the Gemara said that if the Yavam cannot sell after Yibum, all the more so he cannot sell beforehand. If he can decline the enactment before Yibum, this is not a Kal v'Chomer!