Gemara

(Mishnah): If the wall of a Chatzer fell, they must rebuild it to four Amos. (If Reuven built it himself,) we assume that Shimon paid, unless Reuven can prove that Shimon did not pay.

(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!

Question: The Mishnah says that we assume that Shimon paid, unless Reuven proves otherwise. If he says that he paid in the proper time, surely we assume that he did! Rather, he says that he paid early, and that one is believed to say that he pays before the proper time!

Answer: This case is different, because he cannot wait to pay. The payment is due for each row of bricks when it is built!

In practice, Rav Papa and Rav Huna brei d'Rav Yehoshua ruled like Abaye and Rava. Mar bar Rav Ashi ruled like Reish Lakish.

The Halachah follows Reish Lakish.

We apply the Chazakah even against orphans. (If a man died before the time to pay his debt, the lender collects from the orphans without swearing.)

Even though (normally) one collects from orphans only through an oath, here is different, for the Chazakah is that one does not pay before the time.

33a - Rava bar Sharshom: I took land for Mashkanta from Ploni. He owed me also other money as well; he died. After the Mashkanta ended, I did not return the land, lest I need to swear to collect from orphans. I hid the Mashkanta document, to eat the Peros until I collect the other loan as well. Migo I could claim that I bought the land, I am believed to say that they owe me the money.

Abaye: You have no Migo, for people know that it the orphans'. You must return the land. When they grow up, you will claim your debt from them.

Erchin 22a (Rav Asi): Beis Din collects from minor orphans' property only to pay off a loan (from a Nochri) on Ribis.

(R. Yochanan): They collect also to pay a widow's Kesuvah (to exempt the orphans from feeding her).

Question (against Rav Asi - Mishnah): We auction off orphans' property for 30 days. (A Nochri creditor would not consent to wait 30 days!)

Answer: The case is, the Nochri agreed to follow the laws of Yisrael regarding auction, but not regarding Ribis.

Rishonim

Rif and Rosh (1:9): The Halachah follows Reish Lakish, even against orphans. Normally, one does not collect from orphans without swearing. This is an exception, for one does not pay before the time.

Rosh: This is even from minor orphans.

Tosfos (5b DH v'Afilu): We can bring a proof from Erchin 22a, which strained to find a case when Beis Din collects from minor orphans' property, to answer for Rav Asi. It did not say that we collect from them within the time! Presumably, he and R. Yochanan, who adds only a Kesuvah, hold like the Halachah, i.e. like Reish Lakish. Also, Rava said that we rule like Reish Lakish against R. Yochanan in only three (other) places! Even though Rava rules unlike Reish Lakish, the Gemara often cites Rava's teaching (for it is true).

Rebuttal (Gra CM 78:3): The Gemara did not want to give an answer unlike Abaye, Rava, Rav Papa and Rav Huna. We often rely on Rava's rule, but not where the Gemara explicitly says that the Halachah follows Reish Lakish.

Hagahos Maimoniyos (Hilchos Malveh 12:2): We collect from minor orphans' property through a Migo (33a. Abaye rejected the Migo only because it was known that it is not his land.) Since we did not resolve whether or not a Migo helps against a Chazakah, also Chazakah helps to collect from minor orphans!

Rambam (Hilchos Malveh 14:1): One who collects from a minor or adult heir collects only through an oath like a mid'Oraisa oath. 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.

Lechem Mishneh: The Rambam (12:1-3) says that from minor orphans we collect only a Kesuvah. Indeed, here he means only that a Kesuvah can be collected from a minor orphan.

Rosh (ibid., citing the Ramban): Rav Hai Gaon says that one must swear to collect a document from buyers before the time. Perhaps there the concern is greater than when collecting from orphans, for had their father paid, he would have said so before he died. If one says 'I paid within the time', even though he is not believed, the creditor must swear Heses, since the borrower has a Vadai claim. Orphans do not obligate an oath due to Safek.

Hagahos Ashri: The creditor needs to swear only if the borrower demands that he swear.

Magid Mishneh: Admission that a loan was not paid does not allow collecting from buyers, for we are concerned lest it is a scheme. We rely on such admissions to uproot inheritance, for he has no need to lie. He has other ways to uproot inheritance! Regarding the Chazakah that one does not pay within the time, there is no reason to distinguish buyers from heirs.

Mordechai (467,468): A case occurred in which Avraham hired a scribe. The scribe did part of the job, and was killed. His widow claimed food and her Kesuvah from the wages for what he wrote. Avraham said that he paid for more than the scribe wrote. Gedolim ruled that he is believed. Even though the Halachah follows Reish Lakish, that one does not pay before the time, and Sechirus is paid only at the end, the Gemara said that the money for each row of a wall is due when it is completed. Here also, money for each treatise is due when it is finished, even if he was hired to write many. There is no difference if he or his heirs demands his wages. Even if the scribe demanded his wages, Avraham has a Migo, for he could say 'I stipulated to pay you within the time.' For every unsettled monetary law, ha'Motzi mi'Chavero Alav ha'Re'ayah.

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 even from orphans. If Shimon died within the time and left orphans, even minors, Reuven collects without an oath. 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.

Beis Yosef (DH u'Mah she'Chosav Rabeinu): If testimony was not accepted in front of their father, he could not collect until they mature, for testimony must be in front of the defendant, and a minor is as if he was not here. The Rashba (3:200) says that if payment was not due in their father's lifetime, we appoint an Apotropos to pay Reuven without an oath. Even though testimony must be in front of the defendant, we validate a document in the borrower's absence. When a document is validated, it is as if the signatures were validated from when they signed. If the property is in a different place than the orphans, we appoint the Apotropos where the property is.

SMA (4): Chachamim were lenient only about validation of documents (to allow it in the defendant's absence), for it is only mid'Rabanan, but not for acceptance of testimony.

Shach (2): Most Poskim say that this is even for minor orphans. This is primary. They cannot say 'we hold like Maharshach, who says that we do not take money from minor orphans, since Poskim argue about this.' Maharashdam says that we collect from minor orphans only when the payment date was set from the beginning, but not if the date came in the borrower's lifetime, and the lender graciously pardoned him and granted an extension. I disagree. Since it is within the time, in every case he collects.