Gemara

(Mishnah): If one was Makdish his field at a time when Yovel applies, the redemption price is 50 Shekalim for a Beis Kor. Ditches or rocks in it are redeemed like a field only if they are less than 10 Tefachim deep or tall.

Question: (When they are 10, granted they are judged separately from the field, but still) they should be redeemed according to the fixed price!

Answer (Rav Ukva bar Chama): The case is, the ditches are full of water, and cannot be sown. (Therefore, they are not redeemed like fields.)

172a (Rava): If one has two loan documents for 50 each, and wants to convert them to one document of 100, we do not do so. This helps the lender, for (if the borrower paid half,) it pressures the borrower to finish paying (lest the lender claim the entire 100 from him). It helps the borrower, for (if he pays half,) the lender's document will be blemished (and he must swear to collect the rest).

Bava Metzia 77b (Rava): If one paid a debt of 100 Zuz, one Zuz at a time, the debt is paid, but the lender may bear a grudge, for he loses this way.

Kidushin 20b - Question (Rav Huna bar Chinena): If one sold Bayis Ir Chomah (a house in a walled city), can he partially redeem it? Do we learn "Ge'ulaso- Ge'ulaso" from a Sedei Achuzah (a field that one inherited from his ancestors) that was sold, which cannot be partially redeemed? Or, perhaps there the Torah said that partial redemption does not work, but here it did not say so?

Answer (Rav Sheshes - Beraisa): The repetition "v'Im Pado Yifdeh" teaches that one may partially redeem his Sedei Achuzah from Hekdesh;

R. Shimon says, if one sold his field and did not redeem it before Yovel, it reverts to him in Yovel. Therefore, he may not partially redeem it. If one was Makdish his field and does not redeem it before Yovel, it is given to the Kohanim. Therefore, he may partially redeem it.

(Culmination of answer): Similarly, one may partially redeem Bayis Ir Chomah, for after one year, he cannot redeem it.

Avodah Zarah 4a - Question: "Rak Eschem Yodati... Al Ken Efkod Aleichem Es Kol Avonoseichem" - one does not afflict his beloved!

Answer (R. Avahu): I explain through a parable. A man lent to someone he loves and to someone he hates. He collects from his friend bit by bit, he collects from the other all at once.

Erchin 21b: Some prefer to buy orphans' property sold to pay a (Kesuvah of a) woman, for she prefers to receive the money little by little.

Rishonim

Rambam (Hilchos Malveh 23:17): If David had two loan documents of 50 each, and asked to convert them to one document for 100, we do not do so. It is the borrower's privilege that there are two documents, so David cannot force him in Din to pay all at once.

Rambam (Hilchos Mechirah 8:6): If one bought something and paid and erred about the amount, and later the seller says 'you gave to me 90, not 100', the sale is valid, and he pays the remaining 10 even after many years.

Rosh (Bava Metzia 6:8): Rava teaches that the lender cannot demand to be paid at once. We also learn from above; we said that one can pay half the price now, and the rest after several years.

Mordechai (Bava Metzia 352): Some learn from Rava that one can pay a debt one Zuz at a time. Others learn from Avodah Zarah that one cannot. This is not a proof. We can say that he lent to him for a set time. He collects from his friend before the time, bit by bit, and does not collect from the other until it is due, and then he collects all at once. In Erchin we say that a woman prefers to be paid little by little. This connotes that normal creditors do not take a little at a time.

Ran (Kidushin 7b DH Garsinan Taught, and Teshuvas Rashba): If there is no source to say otherwise, we say that one can partially redeem Bayis Ir Chomah. Some derive that one who gave his field for collateral can pay half at a time. However, some say that even regarding Sedei Achuzah, he does not get back half now. It is half redeemed only to ensure that half will not go to Kohanim in Yovel. The Rashbam (103a DH Likadshu) agrees. He explains that we asked 'we should be able to redeem the rocks by themselves, for they are like a separate field!' Even if it is all one field, one can partially redeem it! we must say that one who redeems part of one field receives nothing now. Also the Ramban says so. Surely one may partially redeem without getting back half, for Rava taught that piecemeal payment is payment.

Poskim

Rema (YD 172:3): Any Mashkanta cannot be partially redeemed. If the borrower paid part, the lender eats the Peros until he is fully paid.

Shach (22): This is a textual error. It should say can be redeemed, like Teshuvas ha'Rashba and Shulchan Aruch (CM 74:4).

Gra (15): The text is correct. In this sense (to get back half the Mashkanta), it cannot be partially redeemed. According to the Shach, it should say 'in any case, if he partially redeemed...'

Shulchan Aruch (CM 74:4): If David lent to Levi for a set time, and within the time Levi wanted to repay bit by bit, some say that David cannot demand to be paid only at once. Piecemeal payment is payment, just David has a grievance against him.

SMA (10): David's grievance is 'had you paid me at once, I would have spent the money profitably to buy merchandise.'

Beis Yosef (DH v'Im): The Rif did not bring Rava's teaching. Perhaps he holds that Rava discusses one who accepted piecemeal payment, but one need not accept it. The Rosh says that he must accept payment. Also Ba'al ha'Itur says so. If not, why does he have complaints? If he wants, he need not accept the money! In Kidushin, we say that one may partially redeem Bayis Ir Chomah, unless we learn from Sedei Achuzah.

Shach (17): The Rif explains that Rava teaches that piecemeal payment is valid b'Di'eved, i.e. if David accepted partial payment, he cannot say 'take it back, and you are liable (for any loss) until you pay all of it at once.' The Rambam and Semag rule that if David wants to convert two loan documents of 50 to one document for 100', we do not, for now David cannot force Levi to pay all at once. Sefer ha'Terumos explains that (even with one document) David cannot force Levi to pay all at once. Rather, Levi fears to pay part at a time, lest David deny the partial payment. The Rambam and Semag hold that David can force him to pay at once. We must say that Levi wants to pay partially within the time, and David demands payment all at once. If the loan was already due, even if there are two documents David can force him to pay at once. (The Bach (53:1) understood that the Rambam discusses after payment is due, therefore, he found the Rambam difficult.) The Rambam did not need to bring Rava's law, for Rava discusses b'Di'eved, and it follows from what the Rambam wrote in Hilchos Mechirah. I say that also the Rosh can agree with the Rif. The Rosh says that Rava's law follows from above, that one can pay half the price now, and the rest after several years. This does not show that a lender must accept partial payment l'Chatchilah! However, if so, why did the Tur rule like Ba'al ha'Itur, unlike the Rosh? One can resolve this with difficulty.

Beis Yosef (DH Kosav): The Rashba (3:37) says that if Reuven owed Shimon in currency A, and paid part in another currency B, and now Shimon wants to consider what was paid based on the current value of currency B, and Reuven wants to consider it based on its value at the time he paid, Reuven is correct. What he paid was payment, not a deposit.

Shulchan Aruch (ibid): However, if Levi gave a field or two for collateral, he cannot force David to return half the collateral for half the money.

Beis Yosef (DH u'Mah she'Chosav): Sefer ha'Terumos says so in the name of the Ramban, and that Bava Basra 107a proves this. In Kidushin, we say that one may partially redeem, i.e. pay half the money, but the buyer keeps the field until it is fully redeemed. The Rashbam (DH Likadshu) agrees. Another version of Sefer ha'Terumos says that some disagree. He equates securities of Metaltelim and land.

Taz: In a Stam loan, David eats the Peros and deducts them from the loan. He can say that he prefers to work and eat the Peros of the entire field. If Levi gave a security of Metaltelim, David must return half due to Midas Sedom.

Shach (18): David does not eat the Peros, yet he may keep the field to pressure Levi to pay fully. If David eats the Peros, even after full payment he keeps the field until the set time (Sa'if 3), unless the custom in this place is that the borrower can redeem it early.

Rema: Likewise, if the time for payment came, David need not accept piecemeal payment.

Source (Gra 16): We learn from Avodah Zarah and Erchin.

SMA (11): It is not really likewise! Before payment was due, David must accept piecemeal payment (but he keeps the entire Mashkanta)! The Rema means, just like David has the upper hand before the loan is due regarding the security (he keeps all of it), he has the upper hand after it is due and need not accept piecemeal payment! The Mordechai proves this.