Gemara

(Rava): This (acquiring Metaltelim Agav land) works only if all the money was given. If only part was given, he acquires only according to what he paid.

Support (Beraisa): In some respects, Chazakah is stronger than money or a document. One can acquire 10 fields in 10 lands through one Chazakah. This is only if he gave the money for all of them. If not, he acquires only according to what he gave.

This Beraisa also supports Shmuel.

(Shmuel): If one sold 10 fields in 10 lands, once the buyer acquires one through Chazakah, he acquires all of them.

Bava Metzi'a 77b (Beraisa #1): Reuven sold a field to Shimon for 1000, and Shimon paid 200. If Reuven retracts, Shimon has the upper hand. He can demand his money back, or take Idis (best quantity land) worth 200. If Shimon retracts, Reuven has the upper hand. He can return the money, or give Ziburis (worst quantity land) worth 200.

R. Shimon ben Gamliel says, we teach them not to retract. Rather, they write a document of sale saying that Shimon still owes 800, which he may pay later.

Inference: Without writing this, Shimon would not acquire the field!

Contradiction (Beraisa #2 - R. Shimon ben Gamliel): If Levi bought land and paid half of the price, he acquired it all. He can give the rest of the money years later.

Answer: In Beraisa #1, the seller pursues the buyer to get the money. (This shows that he sold only because he needs the money. Since Shimon cannot pay the full amount, he does not acquire, unless they write...) In Beraisa #2, the seller does not pursue the buyer (so Shimon acquires);

(Rava): If the seller pursues the buyer, the buyer does not acquire (unless he pays right away). If the seller does not pursue the buyer, the buyer acquires.

Question (Rav Acha brei d'Rav Yosef): People cite Rava to say that he acquires!

Answer (Rav Ashi): Rava said so when he sold his field due to its poor quantity.

Rishonim

Rif (Bava Metzi'a 48a and Rosh 6:8): Rava validated a sale (before the money was given) even when the seller pursues the buyer to get the money, if he sold a field due to its inferiority. He pursues the buyer, lest he retract.

Rosh: Even though the buyer cannot retract in any case, the seller fears lest the buyer discover its badness, and Yidchenu b'Damim (refuse to pay).

Rambam (Hilchos Mechirah 1:8): if one sold a house or field or gave a gift, once the receiver locks, fences or breaches a fence, he acquires through Chazakah.

Kesef Mishneh: The Rambam (Halachah 4) says that money acquires where they do not write a document. He did not say that Chazakah works only in certain cases.

Rambam (19,20): If one sold 10 fields in 10 lands, once the buyer makes Chazakah in one, he acquires all of them. This is if he gave all the money.

Magid Mishneh: We discuss where people write documents, so money does not acquire by itself. Chazakah works like a document. Meforshim argue about whether or not one acquires through Chazakah without paying the money. The Rashba says that it does, when the seller does not show anxiety to get the money. Here, he must pay the money because he did not do Chazakah in all the fields.

Question (Rosh Kidushin 1:36): Shmuel taught that if one bought 10 fields in 10 lands, once he acquires one through Chazakah, he acquires all of them. Rava said that this is only if all the money was given. If so, why is Chazakah needed?

Answer (Rosh): We discuss a place where they write documents (so money does not acquire by itself).

Question (Tosfos DH 27b DH ba'Meh): If Chazakah acquires only when he gave the money, this is not a strength of Chazakah over money!

Answer #1 (R. Chananel): Chazakah acquires a gift without money.

Answer #2 (R. Shmuel): The case is, the seller owed the money to the buyer. Just like a debt cannot be Mekadesh a woman, it cannot acquire land.

Rosh: The Gemara connotes that he does not acquire them all because they are in different lands, but Chazakah acquires one field even without money. We may derive that in a place where they write documents, even though money does not acquire, Chazakah acquires. Chazakah is stronger, for one did an act with the property itself. This is like Meshichah, which acquires without money.

Poskim

Shulchan Aruch (CM 192:12): If one sold 10 fields in 10 lands, once the buyer makes Chazakah in one of them, he acquires all of them.

Beis Yosef (DH v'Chosav ha'Rosh b'Perek): The Ran holds that Chazakah acquires by itself when the seller does not pursue the buyer. Sefer ha'Terumos says that some bring proofs that Chazakah is like a document, and acquires only a gift or a field sold due to its inferiority. He disagrees. R. Yerucham says that Chalipin acquires without money, like Chazakah.

Beis Yosef (DH veha'Itur): Ba'al ha'Itur says that where people normally make Chazakah, even money and a document do not acquire until he does Chazakah, and that Rav Hai Gaon also said so.

Rebuttal (Gra CM 192:24): Ba'al ha'Itur learned from Bava Metzi'a. R. Shimon ben Gamliel said that a document is needed to acquire. This is wrong. There, we discuss a seller who pursues the buyer.

Shulchan Aruch (16): Chazakah acquires without money or a document whenever the seller does not pursue the buyer to get the money.

SMA (27): It acquires one field, the same amount that one acquires in a Hefker field. One does not acquire more, even if they are adjacent.

Rema: This is even in a place where they normally write a document. However, if he stipulated, everything is according to his stipulation.