Bava Batra 54B

ושאינה מסויימת במצריה, עד כמה? אמר רב פפא: כדאזיל תיירא דשורי והדר.

And if it is not defined by its boundaries, up to how much of the field is acquired by one strike of the hoe? Rav Pappa said: He acquires as far as an ox driver goes and returns, i.e., the size of a standard furrow, beginning where the hoe entered the ground.

אמר רב יהודה אמר שמואל: נכסי גוי הרי הן כמדבר, כל המחזיק בהן זכה בהן. מאי טעמא? גוי ⁠– מכי מטו זוזי לידיה אסתלק ליה, ישראל לא קני עד דמטי שטרא לידיה. הלכך הרי הן כמדבר, וכל המחזיק בהן זכה בהן.

§ Rav Yehuda says that Shmuel says: With regard to the property of a non-Jew that was sold to a Jew for money, it is ownerless like a desert until the purchaser performs an act of acquisition; anyone who takes possession of it in the interim has acquired it. What is the reason for this? The non-Jew relinquishes ownership of it from the moment when the money reaches his hand, while the Jew who purchased it does not acquire it until the deed reaches his hand. Therefore, in the period of time between the giving of the money and the receiving of the deed, the property is like a desert, and anyone who takes possession of it has acquired it.

אמר ליה אביי לרב יוסף: מי אמר שמואל הכי?! והאמר שמואל: דינא דמלכותא דינא; ומלכא אמר: לא ליקני ארעא אלא באיגרתא! אמר ליה: אנא לא ידענא; עובדא הוה בדורא דרעותא, בישראל דזבן ארעא מגוי, ואתא ישראל אחרינא רפיק בה פורתא; אתא לקמיה דרב יהודה, אוקמה בידא דשני.

Abaye said to Rav Yosef: Did Shmuel actually say this? But doesn’t Shmuel say that the law of the kingdom is the law, i.e., the halakha obligates Jews to observe the laws of the locale in which they reside, and the king said that land may not be acquired without a document? Therefore, taking possession should not be effective for acquisition. Rav Yosef said to him: I do not know how to reconcile this contradiction, but there was an incident in the village of Dura that was founded by shepherds, where there was a Jew who purchased land from a non-Jew by giving money, and in the interim another Jew came and plowed it a bit. The two Jews came before Rav Yehuda for a ruling, and he established the property in the possession of the second individual. This accords with the ruling of Shmuel that the property is ownerless until a Jew performs an act of acquisition.