Related for Sotah 59:1
שלישי הבא מחמת שני דשני גופיה אסור בחולין אינו דין שעושה רביעי בקודש
then that which is unclean in the third degree through contact with what is unclean in the second degree — the second degree which is itself forbidden in the case of non-holy food<span class="x" onmousemove="('comment',' Non-holy food can become unclean in the second degree. ');"><sup>1</sup></span>
Mishnah Challah
Rabbi Eliezer says: Hallah may be taken from [dough] that is clean, [in order to exempt] that which is unclean. How [may this be done]? [If one has] clean dough and unclean dough, he takes sufficient hallah out of the [clean] dough whose hallah has not yet been taken, and puts [dough] less than the size of an egg in the middle, in order that he may take off [the hallah] from what is close together. But the sages prohibit.
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