Bava Kamma 93B

מתני׳ הגוזל עצים ועשאן כלים, צמר ועשאן בגדים ⁠– משלם כשעת הגזלה.

Mishnah: In the case of one who robs another of wood and fashions it into vessels, or one who robs another of wool and fashions it into garments, he pays the robbery victim according to the value of the goods at the time of the robbery, but he need not return the vessels or garments. He has acquired the stolen items because they had undergone a change.

גזל פרה מעוברת ⁠– וילדה, רחל טעונה ⁠– וגזזה; משלם דמי פרה העומדת לילד, ודמי רחל העומדת ליגזז.

If one robbed another of a pregnant cow and it then gave birth while in his possession, or if one robbed another of a ewe that was laden with wool and the robber then sheared it, the robber pays the value of a cow that is ready to give birth or the value of a ewe that is ready to be shorn. He pays the value of the animal at the time of the robbery, and the calf or the wool remains his.

גזל פרה ⁠– ונתעברה אצלו וילדה, רחל ⁠– ונטענה אצלו וגזזה; משלם כשעת הגזלה. זה הכלל: כל הגזלנים משלמין כשעת הגזלה.

If one robbed another of a cow, and it became pregnant in his possession, and it then gave birth; or if one robbed another of a ewe, and it became laden with wool in his possession, and he then sheared it, then the robber pays according to the value of the animal at the time of the robbery. This is the principle: All robbers pay according to the value of the stolen item at the time of the robbery.

גמ׳ אמרי: עצים ועשאן כלים ⁠– אין, שיפן ⁠– לא; צמר ועשאן בגדים ⁠– אין, ליבנן ⁠– לא.

Talmud: The rabbis say: It can be inferred from the Mishnah that if one robbed another of wood and fashioned it into vessels, yes, the robber acquires the wood due to the change. If he merely sanded it, no, the robber does not acquire it, as this is not a significant change. Similarly, if one robbed another of wool and fashioned it into garments, yes, he has acquired the wool due to the change. If he merely washed it, no, he has not acquired it.