הלכה על גיטין 72:16

But the Sages ordained (Bava Kamma 94b), as a result of the Ordinance of the Penitents, that anything that appreciates in the hand of the robber after the forsaking be his. And [so] when he comes to return it, he calculates with the robbed one how much it was worth at the time of the robbery; and the robbed one pays him the money of that which it appreciated, and takes it. And the Sages have the power to do this thing, since they may do according to their will in a monetary matter - and even against the commands of the Torah. As it is well-known that what the court makes ownerless is ownerless (Yevamot 89b, Gittin 36b). And therefore if a gentile (to which the Ordinance does not apply) robbed and [the item] appreciated, whether before the forsaking or whether after the forsaking; or if an Israelite robbed it and he sold [it] to a gentile, and the gentile makes [it] appreciate - [the appreciation is for the one robbed. If he sold it (Minchat Yitschak)] before the forsaking, the law of the [purchaser] is like the law of the [robber] - as transfer of domain does not create acquisition without forsaking. But after the forsaking - whether that forsaking was after the theft came to the hand of the purchaser, or when it was still in the hand of the robber - since there was forsaking and a transfer of domain with this theft, the purchaser has acquired the body of the theft. And if that robber that sold it to him is a robber that is not famous, it is completely his; and he is not obligated to return anything to the one robbed. Rather the robbed one should go and sue the robber. But if he is a famous robber, the purchaser is obligated to return the value of the theft to the robbed one, and he sues the robber.

And one who transgresses this and claimed a debt from his fellow that the seventh year passed at the time of the [Temple] has violated this positive commandment, besides having violated a negative commandment, as we will write in this Order, with God's help (Sefer HaChinukh 475). And at this time [such a one] has done a rabbinic prohibition. And if the court knows that the seventh [year] has passed it, they are not obligated to press [the debtor] at all, and even at this time. And even though the release of monies is only rabbinic today and it is established for us that a lien is from Torah writ (Kiddushin 13b); nonetheless the law is decided that the sages have the power to push off the word of the Torah in any matter of money, due to the [power] of the court to effectively make property ownerless (Gittin 36b).