Bava Kamma 94B

אמרו הלכה כרבי שמעון בן אלעזר. וליה לא סבירא ליה.

Some said that the halakha is in accordance with the opinion of R' Shimon ben Elazar, but Shmuel himself does not hold accordingly.

אמר רבי חייא בר אבא אמר רבי יוחנן: דבר תורה ⁠– גזילה הנשתנית, חוזרת בעיניה. שנאמר: ״והשיב את הגזלה אשר גזל״⁠ – מכל מקום. ואם תאמר: משנתנו! משום תקנת השבים.

The Talmud continues the discussion of acquisition of a stolen item due to a change it underwent. R' Ḥiyya bar Abba says that R' Yoḥanan says: By Torah law, a stolen item that has changed is returned as is, as it is stated: “And he should restore that which he took by robbery” (Leviticus 5:23). This indicates that he should return it in any case, even if it has been changed. And if you say: In our Mishnah it is stated that if the stolen item is changed the robber gives monetary compensation rather than returning the item, that policy was instituted by the rabbis due to the ordinance instituted for the penitent.

ומי אמר רבי יוחנן הכי?! והאמר רבי יוחנן: הלכה כסתם משנה, ותנן: לא הספיק ליתנו לו עד שצבעו ⁠– פטור!

The Talmud asks: But did R' Yoḥanan actually say that? But doesn’t R' Yoḥanan say: The halakha is in accordance with an unattributed Mishnah, and we learned in a Mishnah with regard to first of the sheared wool (Ḥullin 135a): If the owner of the sheep did not manage to give the sheared wool to the priest before he dyed it, he is exempt from giving it to the priest. This indicates that dyeing the wool is a significant change.

אמר להו ההוא מדרבנן ⁠– ורבי יעקב שמיה: לדידי מפרשא לי מיניה דרבי יוחנן ⁠– כגון שגזל עצים משופין ועשאן כלים, דהוה ליה שינוי החוזר לברייתו.

One of the Rabbis, whose name was R' Ya’akov, said to them: It was explained to me directly by R' Yoḥanan that he was referring to a case where he robbed another of sanded wood and fashioned it into vessels, which is a change in which the item can revert to its original state. Consequently, the robber does not acquire the item by Torah law, but rather due to the ordinance instituted for the penitent.