Комментарий к Хала́ 2:8

נטלת מן הטהור על הטמא – and we do not suspect lest they come in contact with each other.

Introduction In this mishnah Rabbi Eliezer finds a way to give hallah from pure dough in order to exempt a separate batch of impure dough.

נוטל כדי חלה – the measure of Hallah that one needs to take from the pure and the impure, he takes from that pure dough whose Hallah had not been ritually dedicated.

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. The problem in this situation is how to join the two batches of dough together so that one hallah can be taken from both, without causing the pure dough to become impure. He cannot just take from one to exempt the other because hallah taken from one batch of dough cannot exempt a separate batch of dough. This is how Rabbi Eliezer suggests it may be done. First, he takes a sufficient measure of hallah from the clean dough in order to exempt both batches of dough. He does this at the outset lest the clean dough is made impure at least he now has enough clean hallah to exempt both batches. Then in between the two batches he puts an amount of dough less than the size of an egg. This serves to attach the two batches, but because it is less than an egg’s worth in volume, the impurity is not conveyed across to the pure dough. Now, the hallah that he took from the pure dough counts to exempt the impure dough.

ונותן פחות מכביצה באמצע – whether ritually impure or pure, for less than an egg’s bulk does not defile, and they set aside the Hallah on that which is less than an egg’s bulk which connects between the impure anad the pure, for the Hallah does not receive ritual impurity in this.

But the sages prohibit. The other rabbis prohibit one from separating hallah from pure dough for impure dough, lest he unwittingly causes the pure dough to become impure. Rather he should take pure hallah from the pure dough and impure hallah from the impure dough.

כדי שיטול מן המוקף – that the ritually impure is attached to the ritually pure on that which is less than an egg’s bulk, and it is as if the ritually impure and the pure [are found] in one [piece of] dough.

וחכמים אוסרין – to take from the ritually pure on that which is impure, and we are suspect lest they come in contact with each other, but he should take from the ritually pure to itself, and from the ritually impure to itself. And the Halakha is according to the Sages.