Terumot, Chapter Three, Mishnah Five
This mishnah discusses ways in which one can designate terumah or tithes within a pile of produce.
1) If one says: The terumah of this pile is within it, or, its tithes are within it, or, the terumah of tithe [terumat maaser] is within it:
a) Rabbi Shimon says: he has thereby designated it.
b) But the sages say: not unless he said, It is in the north or south of it.
2) Rabbi Elazar Hisma says: one who says, The terumah of this pile is taken from it for it, he has thereby designated it.
3) Rabbi Eliezer ben Yaakov says: one who says, The tenth part of this tithe is terumah of tithe for that pile, he has thereby designated it.
Section one: According to Rabbi Shimon, if one says that the terumah, tithes or terumah taken from tithes [terumat maaser] is in a pile of produce but does not actually point out where in the pile the terumah, tithes or terumat maaser are, he has successfully designated them and the pile is no longer untithed produce. He can eat from the pile, as long at some point he removes that which he designated.
The sages disagree and hold that he must set aside a place within the pile where the terumah, tithes and terumat maaser are. It is not enough just to say, within it.
Section two: Rabbi Elazar Hisma says that one doesnt even need to say within it. In other words, whereas Rabbi Shimon says that he must at least designate that the terumah is within the pile, for Rabbi Elazar Hisma it is sufficient just to say that one has set aside terumah for a given pile of produce.
Section three: Rabbi Eliezer ben Yaakov agrees with Rabbi Elazar Hisma and says that the same is true when it comes to separating terumat maaser from tithe. He need not say within itas long as he says he is separating it, he has successfully designated it.