Gemara

87a (Mishnah): If a (married) woman damaged someone, she is exempt now, but pays later.

89a - Question: Granted, we can say that she has no Nichsei Melug. However, she should sell the Tovas Hana'ah of the Kesuvah to pay the damage!

Answer: She need not sell it, for Shmuel taught that one who sold a loan document can pardon it. (Surely, she will pardon it to please her husband!)

Kesuvos 19a (Rav Yehudah): If he says that the document is Amanah (the borrower gave it to the lender before the loan was given, and trusted that he will not claim with it improperly), he is not believed.

(Abaye): The lender says that it is Amanah. It is a case where his admission hurts others (his creditors), like R. Noson's law:

Beraisa (R. Noson): "He will give to the one he sinned against" - if Reuven owes Shimon, and Shimon owes Levi, we take from Reuven to pay Levi.

81b (Beraisa): Reuven owed money to his brother Levi. Levi died and his wife fell to Yibum. Reuven cannot say 'since I (will do Yibum and) inherit, I will keep the money.' Rather, we take the money and buy land with it, and he eats the Peros.

Rav Nachman said that this Beraisa is erroneous. This is not because he can say to her 'you have no claim against me.' Perhaps the Beraisa is like R. Noson!

Bava Basra 147b - Question: Granted, if Matnas Shechiv Mera is mid'Oraisa, the heir cannot pardon it. (It is unlike sale of a debt, which is only mid'Rabanan). But if Matnas Shechiv Mera is only mid'Rabanan, why can't the heir pardon it?

Rishonim

Question: Why isn't Shimon believed to say that the document was Amanah, Migo (since) he could pardon the debt? One who sold a loan document can pardon it!

Answers #1 (Rosh and Tosfos, Kesuvos 2:9 and 19a DH u'Chegon): This is not a Migo, for perhaps he plans to collect. He assumes that the borrower does not want to steal, and will pay later.

Answer #2 (Ramban, brought in Magid Mishneh Hilchos Malveh 1:4): There is a Chazakah that what a person has belongs to him. We do not believe a Migo against a Chazakah, especially since people are prone to scheme to deprive other people of their rights to collect.

Answer #3 (Tosfos, ibid.): If the sale of a loan document is only mid'Rabanan, perhaps one cannot pardon when Shibud d'R. Noson applies, for it is mid'Oraisa.

Ran (Kesuvos 6a DH l'Olam): When Shibud d'R. Noson applies, Shimon cannot pardon the debt, because Levi has a lien against Reuven.

Beis Yosef (CM 86 DH v'Da): The Rif holds that the sale of a loan document is only mid'Rabanan. R. Tam holds that it can be pardoned because the lender keeps Shibud ha'Guf (the borrower owes him; he sold only collection rights). The Rosh brought only Tosfos' first answer. He holds that one can pardon when Shibud d'R. Noson applies (he said differently in a Teshuvah). Sefer ha'Terumos says that the Ramban says that one can pardon.

Question: In Bava Kama (87a), we say that a woman need not sell her Kesuvah to pay for damage, for she would surely pardon it. She cannot, due to Shibud d'R. Noson!

Answer (Ran, ibid.): Shibud d'R. Noson applies only when it is time to collect the debt. Surely it does not apply to a Kesuvah, which might never be collected (if she will die first)!

Shach (CM 86:11): The Ritva (Kesuvos 19a DH Omar) says that Shibud d'R. Noson does not apply to a Kesuvah, for it might never be collected. We may not infer that when Shibud d'R. Noson applies, one can pardon before the debt is due. The Rashba (1112) says that before it is due he can pardon, but after it is due Beis Din collects (gives Shimon's document to Reuven). He holds that one can pardon even after it is due, unless Beis Din already collected. I say that Shibud d'R. Noson applies even to a Kesuvah. Why should we distinguish because it might not be collected? In any case, her husband is Meshubad! Also the Ramban says so. Once she damages, her husband is Meshubad due to R. Noson's law. If she sells her Kesuvah to pay the damagee, this is like any sale of a loan document, and she can pardon it.

Question (Tumim 10): We cannot compare a willful sale to forced collection of Beis Din! If Beis Din collected land for a creditor, and then we found that it was not the borrower's, surely the creditor's Shibud did not lapse! Here also, her pardon uproot the Shibud, so the collection was invalid!

Answer (Ketzos ha'Choshen 6 and 424:3): This collection was not mistaken. Her Kesuvah was valid, just later she damaged it by pardoning it. The Rashba says so (in Shitah Mekubetzes Kesuvos 19a DH veha'Ramban).

Shach (11): Whenever Shibud d'R. Noson applies, if Shimon sold the document to Reuven (his creditor), he can then pardon it.

Question (Tumim 10): Shimon cannot pardon, because Shibud d'R. Noson gives Shibud ha'Guf to Reuven. Selling to Reuven does not weaken Reuven. Shimon's Shibud to Reuven ends, but Levi is still Meshubad to Reuven!

Answer (Ketzos ha'Choshen 6): Since Shimon's Shibud to Reuven ceased, Shibud d'R. Noson no longer applies.

Hagahos Ashri (Bava Kama 4:4): Reuven cannot pardon Levi and make Shimon lose.

Poskim

Shulchan Aruch (CM 86:5): Shimon cannot pardon Levi or extend the time he has to pay, for Shimon's Shibud on Levi was uprooted. Levi is now Meshubad to Reuven. Similarly, if Shimon says that the document is Amanah or was paid, he is not believed to make Reuven lose.

Source (Gra 16): Bava Basra 147b says that one cannot pardon a debt transferred mid'Oraisa. Shibud d'R. Noson is mid'Oraisa!

Rebuttal (Gra 66:110): Those who disagree hold that one can pardon a debt transferred mid'Oraisa. However, if Matanas Shechiv me'Ra were mid'Oraisa, also the recipient would be like an heir; the giver's child is no better than him.

SMA (9): This is only when Shimon's document says that he is believed. If not, since Levi says that he paid, one who collects from him must swear. Since Shimon agrees that it was paid, Reuven, who collects due to Shimon's power, could not collect.

Shach (11): Many hold that Shimon can pardon, i.e. the Rosh (Kesuvos 2:9), Tosfos' first answer, Ba'al ha'Ma'or and Milchamos Hash-m (Kesuvos 6a). The primary opinion is that he cannot pardon. Kesuvos 81b proves that according to R. Noson, Levi cannot say 'you have no claim against me', for Reuven becomes his creditor. Therefore, Shimon cannot pardon. Saying that a document was paid is pardon, and even more so saying that it was Amanah! Since he is not believed, this shows that he cannot pardon it. R. Chananel says that one who sells a loan document can pardon it, for he can say that he later realized that it was (Vadai, or perhaps) paid. Here he cannot say that it was paid, so he cannot pardon. Others say that one can pardon a sold document because the sale is mid'Rabanan, or he retains Shibud ha'Guf. These do not apply here. Sefer ha'Terumos cites Tosfos to say that Shibud d'R. Noson applies only after coming to Beis Din, but beforehand one can pardon. We do not hold like this.