Bava Batra 125A

מאי שנא מעות דלא ⁠– דלאו הני מעות שבק אבוהון; קרקע נמי ⁠– לאו הא קרקע שבק אבוהון!

because what is different about money, resulting in the halakha that the firstborn is not entitled to a double portion of it, is that their father did not leave them this specific money that was collected. With regard to land as well, their father did not leave them this specific parcel of land when he died, as the debtor could have repaid them with a different parcel of land, or with money.

ועוד, הא את הוא דאמרת: מסתבר טעמא דבני מערבא, דאי קדים סבתא וזבנא ⁠– זבינה זביני!

And furthermore, aren’t you the one who said that the explanation of the people of the West, Eretz Yisrael, is reasonable? In a case where a married woman had been fit to inherit from her great-grandmother but then predeceased her great-grandmother, who then died, and her widower claims the inheritance in his late wife’s stead, the rabbis of Eretz Yisrael ruled that he is not entitled to the inheritance, as it is merely property due to his wife, and a husband does not inherit property due to be inherited by his late wife. Rabba agreed that the inheritance is considered property due to the wife, and not property possessed by her, as if the great-grandmother would have sold it before she died, her sale would have been a valid sale. Here, too, the land should be considered property due to the father, of which a firstborn is not entitled to a double portion, since the debtor could have sold it. Therefore, Rabba’s opinion is difficult.

לרב נחמן קשיא, מאי שנא קרקע דלא ⁠– דלאו הא קרקע שבק אבוהון; מעות נמי ⁠– לאו הני מעות שבק אבוהון!

Abaya continues: According to the opinion of Rav Naḥman it is difficult; what is different about land, resulting in the halakha that the firstborn is not entitled to a double portion of it, is that their father did not leave them this specific parcel of land. With regard to money as well, their father did not leave them this specific money when he died.