Reference for Bava Batra 249:2
ועוד (הא את הוא דאמרת) מסתבר טעמא דבני מערבא דאי קדים סבתא וזבנא זבינה זביני
[why he] does not [take a double portion if] money [was collected]? [Is it not] because their father did not bequeath that particular money? [In the case of] land also, their father, [surely], did not bequeath that land! Furthermore, you, O Master, have said, [that] the reason of the Palestinians is logical, for if the grandmother had sold [her estate] before [her death], her sale would have been valid.<span class="x" onmousemove="('comment',' V. infra 125b. This shows that land, though regarded as pledged, is not considered to be in possession of the creditor since the debtor can dispose of it and meet his liability in another manner; how, then, could Rabbah state that the firstborn if land was collected, receives a double portion? ');"><sup>2</sup></span>