Leviticus 25:30

And if it be not redeemed within the space of a full year,
&c.] Either by the seller or any man of kin to him:

then the house that [is] in the walled city shall be established for
ever to him that bought it, throughout his generation;
after twelve months were elapsed it was not redeemable by any, but to be held by the purchaser and his heirs for ever:

it shall not go out in the jubilee;
from the purchaser or his heirs, to the seller or his heirs; for houses were not like lands, the gift of God, and held under him, but were built by men, and were their absolute property, and therefore they could dispose of them, and they that bought them could hold them after the above mentioned time; nor was there any danger of confounding tribes and families by retaining them: this law was made to encourage persons to settle in walled towns, to make and keep them populous, and to make owners of them careful not to sell them: the Jewish canon is this; when the day of the twelfth month is come, and it (the house) is not redeemed, it is absolutely his, whether he bought it or whether it was given him, as it is said, ( Leviticus 25:30 ) ; and if in the beginning of the day of the twelfth month he (the purchaser) hides himself, that it may be confirmed to him or be his absolutely; Hillel, the elder, ordered that he (the seller) should put his money in the chamber (belonging to the sanhedrim) and break open the door, and go in; and when he would, he (the purchaser) might come, and take his money ^F9; but otherwise, if he suffers this time to pass it is irredeemable, nor will the year of jubilee help him: the Jews except the city of Jerusalem from this law, because, they say, that does not belong to any tribe ^F11.