Reference for Sanhedrin 225:2
אלא לעולם בטהור וכגון דנפול מחיצות וכדרבא דאמר רבא מחיצה לאכול דאורייתא לקלוט דרבנן וכי גזור רבנן כי אתנהו למחיצה כי ליתנהו למחיצה לא:
— But in reality, it refers to undefiled [second tithe], the circumstances being that the barriers of Jerusalem had fallen. And this is in accordance with Raba's dictum. For Raba said: The law of the walls [of Jerusalem], in that it [the second tithe] must be eaten within them, is Biblical; but that they have retaining power,<span class="x" onmousemove="('comment',' I.e., that once within the precincts of Jerusalem, the second tithe is retained by the walls and cannot be redeemed and taken out. ');"><sup>3</sup></span> is merely Rabbinical. Now, when did the Rabbis decree this? Only as long as the walls exist; but if the walls are gone [having fallen], the decree does not hold good.<span class="x" onmousemove="('comment',' Hence, in this case, since it actually belongs to the condemned city, and Jerusalem cannot assimilate it to itself, because its walls had fallen, it must be destroyed; but being sacred, it is hidden instead of burnt. ');"><sup>4</sup></span>