Gemara

(Rav Huna citing Rav): If Reuven denied owing money to Shimon and swore, and later, witnesses said that he owes Shimon, he is exempt;

"The owner will take, and he (the defendant) will not pay" - once the owner received (heard) an oath, the defendant need not pay.

(Rava): Presumably, Rav's law applies only to a loan, for a borrower acquires the money. One can say that the oath is in place of repayment. A deposit always belongs to the owner, Reuven cannot acquire it through an oath!

However, Rav said his law even regarding a deposit, for the verse he expounds discusses a deposit!

Question (Rav Acha bar Minyomi - Mishnah): If Levi accepted (answered 'Amen' to) an oath that the deposit he was guarding for Yehudah was lost; and witnesses testified that he ate it, he pays principal.

Answer (Rav Nachman): The case is, he swore outside of Beis Din.

Rav Acha asked from the Seifa, and Rav Nachman answered that in the Reisha, Levi swore (in Beis Din) before Beis Din told him to. In the Seifa, Beis Din administered the oath. (Rav discusses such a case.)

Rami bar Chama (to Rav Nachman): You do not hold like Rav. What forces you to (strain to explain the Mishnah in such a way to) answer for him?

Rav Nachman: I just explain how Rav must learn the Mishnah.

Question: Rav learns from a verse. How can anyone argue with him?

Answer: The verse teaches that in every oath mid'Oraisa, the oath exempts one from paying. The one who is asked to pay swears and is then exempt. "The owner will take (hear the oath) and he (the Shomer) will not pay" - the one who was asked to pay, he swears.

(Rava): Rav taught that he does not pay. He did not discuss when he admits. It says "he will confess" - whether he originally swore that it was lost or stolen, he must pay the principal and the Chomesh (and bring an Asham)!

Also, if he claimed that a deposit was stolen, and witnesses testified that he stole it, Rav admits that the Torah obligated him to pay Kefel! Rav's law is only when he claimed and swore that it was lost, and did not admit, and witnesses testified that he stole it.

Sanhedrin 25a: Ploni testified 'I saw Bar Binisus borrow on Ribis', and Almoni testified 'I borrowed from Bar Binisus on Ribis.' Rava disqualified Bar Binisus.

Question: Rava said that one who borrows on Ribis is disqualified. If so, Almoni is a Rasha - "Al Tesht Rasha Ed"!

Answer: Rava ruled according to another of his teachings, that one is considered a relative with respect to himself, so he cannot disqualify himself by saying that he is a Rasha.

Kesuvos 87a (Mishnah): A woman must swear (mid'Rabanan) to receive her Kesuvah if one witness says that it was paid.

88a (Rav Papa): If he is clever, he will force her to take an oath mid'Oraisa. He pays the Kesuvah again in front of a different witness. He joins the two witnesses, and claims that the first payment was a loan.

Bava Metzia 26a (Rav Nachman): If two people were standing together and Levi saw a coin fall from one of them, he must return it. The loser does not despair. He is sure that his companion took it, and he plans to confront him and get it back.

Bava Basra 46a (Mishnah): A craftsman does not get a Chazakah.

This implies that someone else gets a Chazakah. We cannot say that witnesses saw the object deposited. If so, no one would get a Chazakah!

Rishonim

Rif and Rosh (9:27): Rami bar Chama asked Rav Nachman 'you do not hold like Rav. What forces you to strain to explain the Mishnah to answer for him? Rav Nachman said that he just explains how Rav must learn. This shows that the Halachah does not follow Rav. His verse teaches that every Torah oath exempts one from paying. The Halachah follows Rav Nachman. Even if one witness came, he swore mid'Oraisa, and another witness came, he must pay.

Yam Shel Shlomo (9:47): Regarding paying, even the first witness joins. It is as if the witnesses came together. You cannot say that Rav Nachman agrees to Rav when only one more witness came (that the oath exempted him), for the Gemara asked 'Rav expounded a verse!' We did not say that the verse teaches about when only one more witness came.

Rambam (Hilchos To'en 2:11): If Levi denied David's claim and swore mid'Oraisa or Heses, and witnesses came and testified that he swore falsely, he must pay and he is established to be suspected to swear falsely.

Rosh (Bava Metzia 2:9): If one is sure that Ploni stole from him, he does not despair, for he can seize Ploni's property, even if he made Ploni swear Heses.

Teshuvas Rosh (8:5): If Reuven swore to Shimon that he does not owe to him anything, and later Reuven's money came to Shimon, he can say that he wants to keep it for what Reuven owes him, for he swore falsely. The Halachah follows Rav Nachman, who says that one who swore did not acquire. Just like if witnesses came afterwards, he is liable, also if Reuven's money came to Shimon's hand, he may seize it, for Reuven still owes b'Yedei Shamayim. Shimon swears that he does not have anything of Reuven's.

Poskim

Shulchan Aruch (CM 87:29): If Levi totally denied David's claim and one witness contradicted Levi and Levi swore to contradict the witness, and afterwards David brought another witness, he joins with the first. Levi pays, even though he swore. He became suspected to swear falsely through two witnesses.

Shulchan Aruch (30): Even though after Levi swore he is exempt, if David seized the money without witnesses, and claims that he took it for his claim because Levi swore falsely, he is believed through a Migo. I.e., he could have said that he did not seize anything. David swears Heses, and he is exempt. We need not say that if David brought two witnesses after Levi swore mid'Oraisa or Heses, that we take from Levi to pay David, and Levi becomes suspected to swear falsely, through witnesses.

Beis Yosef (DH Af): Sefer ha'Terumos and the Rosh say that since the oath does not acquire, seizure helps.

SMA (90): "The owner will take, and he will not pay" means that Beis Din does not force him to pay. It does not discuss when he himself took the money and he has a Migo, or when witnesses came later.

Gra (101): We learn from Bava Basra 46a that if witnesses saw him seize, he is not believed.

R. Akiva Eiger: If Yosef was obligated to swear to Moshe, and said 'you may swear and collect', and Moshe swore, and afterwards Yosef says 'I know that you swore falsely. Now, I will swear (and not pay)', he is believed to do so, Migo he could say 'I paid you.' Mekor Baruch (22) says so, but it seems that Tzemach Tzedek 7 disagrees.

Pischei Teshuvah (32): Tzemach Tzedek 7 says that since Yosef could have sworn to exempt himself, but allowed Moshe to swear, it is as if he said 'if you will swear, I will believe you.' Therefore, he cannot retract. However, he believed him only against himself. If witnesses testify against Moshe, Yosef collects.