Nedarim 47B

או דילמא משום דחילופין כגידולין דמי, לא שנא הוא ולא שנא חברו.

Or perhaps the prohibition on replacement produce in the Mishnah is due to the fact that replacements of the produce are viewed as being like that which grows from them? They are both forbidden because they derive from the forbidden produce. If this is the case, it is no different for him and it is no different for another. Neither may derive benefit from the replacements.

אמר רב אחא בר מניומי, תא שמע: האומר לאשתו ״קונם שאני נהנה ליך״, לווה ובעלי חובין באין ונפרעין. מאי טעמא בעלי חובין נפרעין ⁠— לאו משום דחילופין לאו כגידולין דמי?

Rav Aḥa bar Minyumi said: Come and hear a proof from a baraita: With regard to one who says to his wife: Benefiting from me is konam for you, she may nevertheless borrow money to sustain herself, and the creditors can come and collect her debts from her husband. What is the reason that the creditors can collect from the husband? Is it not because she benefits only indirectly, and it must be that replacements, i.e., the creditors’ money, are not like that which grows from the original item?

אמר רבא: דילמא לכתחילה הוא דלא, ואי עבד ⁠— עבד.

Rava said: This is not proof: Perhaps it is the case that one should not benefit from replacements ab initio, but if one did it, it is done after the fact. Since the wife lacks any other means to support herself, the case is considered to be after the fact, and it is permitted for her to benefit indirectly. Still, replacements of an item are considered to be like that which grows from it ab initio.

אלא, תא שמע: המקדש בערלה ⁠— אינה מקודשת. מכרן וקידש בדמיהן ⁠— הרי זו מקודשת. הכא נמי: לכתחילה הוא דלא, ואי עבד ⁠— עבד.

Rather, come and hear a proof from another Mishnah (Kiddushin 56b): With regard to one who betroths a woman with fruit of orla, i.e., fruit of the first 3 years of a tree’s growth, from which it is forbidden to benefit, she is not betrothed because the fruits have no value. Betrothal can be performed only with an object worth at least one peruta. But if he sold them and betrothed her with the money he received, she is betrothed. Evidently, replacements of a forbidden item are permitted. The Talmud responds: Here also, one should not benefit from the replacement items given in exchange for the orla ab initio, but if one did it, it is done after the fact. Replacements of an item may still be considered to be like that which grows from it ab initio.