Bekhorot 11B

ממורחין מן הגוי, מעשרן והן שלו.

that is gathered in smoothed piles, from a non-Jew, he tithes the piles but they are his, as he is not required to give the teruma to a priest or the tithes to a Levite.

דמרחינהו מאן? אילימא דמרחינהו גוי ⁠— ״דגנך״ אמר רחמנא, ולא דגן גוי!

The Talmud asks: Who smoothed the piles? If we say that a non-Jew smoothed them, doesn’t God state: “Your grain” (Deuteronomy 12:17, 18:4), with regard to teruma and tithes, indicating that only grain whose processing is completed by a Jew is subject to the rules of teruma and tithes, but not the grain of a non-Jew?

אלא דמרחינהו ישראל מרשות גוי. מעשרן, דאין קנין לגוי בארץ ישראל להפקיע מיד מעשר, והן שלו ⁠— דאמר ליה: קאתינא מכח גברא דלא מצית (אישתעית) [אישתעויי] דינא בהדיה.

Rather, clearly a Jew smoothed them while they were in the possession of the non-Jew before purchasing them. Therefore, he tithes them, as a non-Jew has no capability of acquisition of land in Eretz Yisrael that would cause the abrogation of the sanctity of the land, thereby removing it from the obligation to tithe its produce. But the tithes are still the Jew’s, as he says to the priest: I have come to own this produce on the basis of the rights of a man with whom you cannot engage in litigation, i.e., a non-Jew, from whom I bought the produce. Since he is not obligated to give teruma or tithes to the priest, I am not required to give them either.

תנן התם: המפקיד פירותיו אצל הכותי ואצל עם הארץ, בחזקתן למעשר ולשביעית.

§ The Talmud cites an additional discussion involving this issue: We learned in a Mishnah elsewhere (Demai 3:4) that with regard to one who deposits his produce with a Samaritan or with one who is unreliable with regard to tithes [am ha’aretz], when they return it to him, the produce retains its presumptive status with regard to the halakhot of tithe and produce of the Sabbatical Year, both of which must be removed from one’s property. The Samaritan or am ha’aretz is not suspected of having exchanged the deposited produce with untithed produce or produce of the Sabbatical Year.