GEMARA

44b (Mishnah): If a worker says that he was not paid, he takes an oath mid'Rabanan and collects.

45b: This is because an employer is busy, and he forgets, i.e. before the payment date comes. When it comes, he motivates himself and remembers. There is a Chazakah that an employer will not transgress "Lo Salin", and that a worker does not delay claiming his wages. Only one Chazakah supports the worker, that we do not suspect him of stealing.

(Shmuel): A worker swears and collects only if witnesses know that he was hired. If not, the employer is believed, Migo he could say that he never hired him.

Bava Basra 5a (Reish Lakish): If Levi fixed a time to pay his debt to Yehudah, and claims that he paid within the time, he is not believed. We are happy if people pay on time. We do not believe that he paid early!

(Abaye and Rava): He is believed. Sometimes one gets the money and is eager to pay, lest he lose the opportunity!

The Halachah follows Reish Lakish.

Question: If Shimon claimed payment from Reuven after the set time, and Reuven said that he paid before the set time, what is the law?

Do we believe Reuven due to a Migo (if he wanted to lie, he could have lied better, and said that he paid on the set day), even though this opposes a Chazakah (that one does not pay before the time)? Or, we do not believe a Migo that opposes a Chazakah?

RISHONIM

Rif and Rosh (Bava Basra 3a and 1:9): If Shimon claimed payment from Reuven after the set time, and Reuven said that he paid before the set time, the Gemara did not resolve whether or not we believe a Migo against a Chazakah. In all such cases, the Nitva need not pay. Therefore, he swears Heses, and he is exempt.

Hagahos Ashri: If he says that he paid on the day it was due, he is believed. If on the day payment is due, Reuven says 'I paid you within the time', he is not believed through Migo that he could have said 'I paid you today', for this is brazenness. Had he paid today, people would know. It is common to say 'I paid yesterday, and you forgot.'

Rosh: Rashi (5a DH Ad) explains that we assume that Shimon paid, unless Reuven can prove that he did not pay, i.e. witnesses say that Reuven demanded payment and Shimon did not pay. This is astounding. Is there is a permanent Chazakah that he did not pay, just because (once) he did not pay immediately when requested?! Even if he told the witnesses 'I do not want to pay him', perhaps he was just stalling until he will have the money! This is like Rashi explained in Bava Metzia (17a), that if Beis Din told Ploni to pay Levi, and witnesses saw that he refused to pay him, Ploni is never believed to say that he paid him without witnesses. I disagree.

Rambam (Hilchos Malveh 14:1): In the following cases, one collects only through an oath like a mid'Oraisa oath: a loan document was partially paid; one witness testifies that it was paid; he seeks to be paid in the borrower's absence; a creditor collects land bought from the borrower, or from a minor or adult heir. If the debt was for a time and he demanded payment before the time, he collects without an oath. After the time, he collects only with an oath.

Mordechai (470): If Reuven demanded payment before the time, and Shimon said 'I paid you', and Reuven claimed again after the time, and Shimon said 'now, I paid you', Rabeinu Yakir was unsure if he is established to deny. Perhaps he can say 'indeed, I paid you within the time. Since I was not believed, I paid you again after the time!' My Rebbi says that he is established to deny. Rabeinu Meir applies the Chazakah everywhere, except against witnesses, and against a Migo was not resolved. One is not believed to say that he paid within the time Migo he could say 'you pardoned me', for pardon is a poor claim. However, after the time he is believed to say 'you pardoned me', Migo he could say that he paid after the time.

Note: I would think that if one needed to pay again because he was not believed about the first payment, he would be careful to get a proof the second time he paid!

POSKIM

Shulchan Aruch (CM 78:1): If a time was fixed for a debt, and Reuven demanded payment before the time, and Shimon said 'I paid you', he is not believed. There is a Chazakah that one does not pay before the time. This is if there was a loan document, or even if it was a Milveh Al Peh and Reuven took Shimon to Din and the testimony was accepted in front of Shimon.

Bedek ha'Bayis: The Tur and Sefer ha'Terumos say that if he demanded payment at the beginning of the day it is due, the Chazakah is that he did not pay. This is astounding, for we concluded that one is apt to pay on the day it is due. This implies even at the beginning of the day! It is difficult to say that they mean the very beginning, before there was time to pay this day. Also, later they say 'if he claimed at the end of the day...' This implies that before the end of the day, he is not believed. The Gemara connotes that the day for payment is like after the time, like the Rambam in Hilchos Sechirus. Tosfos (5a DH u'Vo) says like Sefer ha'Terumos. The Ramban says so in the name of some of his Rebbeyim and the Ra'avad, but he disagreed.

Gra (6): We know that it is even for a Milveh Al Peh from the Gemara's questions against Reish Lakish.

Shulchan Aruch (ibid): This is only if witnesses saw the loan and the fixing of the time. If not, Shimon is believed through Shevu'as Heses, Migo he could have said that he never borrowed, or that no time was fixed, or that the time passed and he paid at the time.

Source (Gra 7): We learn from Shevuos 45b. A worker can swear that he was not paid only if witnesses know that he was hired. If not, the employer has a Migo. Even though there two Chazakos support the employer and only one supports the worker, and the Chazakah here (that one does not pay before the time) is stronger, since we asked whether it overrides the Migo, since we did not resolve this, and we are lenient (not to collect), the same applies when there are no witnesses.

Shach (6): If there is one witness about the date and the borrower claims that he paid within the time, he is obligated to swear but he cannot (for he does not contradict the witness), so he must pay.

Shulchan Aruch (ibid): If Reuven demanded payment before the time, and Shimon said 'I paid you', and Reuven claimed again after the time, and Shimon said 'now, I paid you', he is established to deny, and he is not believed.

Shach (7): Why is he established to deny? He can say 'indeed, I paid you within the time. Since I was not believed, I needed to pay you again after the time!' Rabbeinu Yakir was unsure about this.

Gra (8): This opinion holds that a Chazakah is like witnesses. We say so (he is established to deny) when witnesses refute him (Bava Metzia 17a). However, we do not apply Migo against witnesses, and Migo helps against Chazakah (since the question was unresolved, we are lenient)!

Shulchan Aruch (5): If he claimed after the time or at the end of the day the time finished, and the borrower said that he paid within the time, he swears Heses and he is exempt.

Beis Yosef (DH v'Chosav Od): Sefer ha'Terumos says that this applies to a Milveh Al Peh. If one has a document, even after the time he swears and collects, like any document (at the time it is due).

Shach (19): He is believed Migo he could have said that he paid within the time. The Gemara did not resolve whether the Migo overrides the Chazakah; the Poskim say that we are lenient for the Nitva. If so, if the lender seized the money, he keeps it in cases where seizure helps for unsettled questions. Also, if he seized without witnesses, he need not swear, due to the Chazakah that one does not pay within the time. I hold that he must swear after he is paid, i.e. Heses. (Normally, one who seizes must swear while holding a Kodesh item.) The Ramban (Bava Basra 40a DH v'Iy) says that acts of Beis Din are as if they are written, and one may collect from Meshubadim, but one is believed to say that he paid within the time, even if Beis Din fixed a time, for one often pays within the time Beis Din fixed. What is his source to distinguish based on who fixed the time?

Note: The SMA (1) said that the Chazakah is only when he fixed a time, for this shows that the borrower needed the money until then.