Nedarim 59
The Gemara says that Tevel for Trumos Maaser that was planted and grow, one needs to take off for only the amount of the original Tevel (and we don't say that it's Batul to what grows) since we have a Pasuk (as the Ran explains) that says only Heter that's planted turns into the next crop, but not seeds that are Assur (because of Tevel.)
Ran points out this must be only an Asmachta. Since we refer to things that don't disappear when it starts growing. We know all things that are Chayiv from the Torah, its seed disappears when you plant it and grows. So, we must say the real reason they Assured it, since what you planted was Issur(Tevel) and what grows afterwards is also Issur (either Tevel or Shvious.) Therefore, just as we said (last week, by Davar Sheyesh Lo Matirin) that Heter cannot Mivatel Heter. So too, Issur cannot Mivatel Issur.
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