in menachot - (I believe) there is a gm which holds that if someone brings a korban on shabbos - fatter/better than the one he already brought and was already yotze the mitzvah - he is not chayev as the "zeh Kaili..." is even a heter for this case. If so, then the gm in Shabbos 137 re: going back and cutting tzitzin sheinom meakvin should also be not chayev. If this is true - is there a Machloket between the two gemorrahs?
aurel littmann, nyc,USA
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Aurel, Baruch she'Kivanta! Your question is asked by the Acharonim.
First of all, I will just point out that it probably would be better to change the references above from 137 to 133. Even though the Mishnah (end of 137a) discusses what the Tzitzin ha'Me'akvin are, the Beraisa on 133b talks about going back and cutting the Tzitzin she'Einam Me'akvin.
1) The Gemara is in Menachot 64a. The Gemara states that if he slaughtered a thin animal on Shabbos, we say to him l'Chatchilah that he should "bring a fat one."
The Teshuvos Sha'agas Aryeh #50 resolves the problem by asserting that on a weekday also, once one has stopped cutting the Tzitzin she'Einam Me'akvin, there is no Hidur Mitzvah to go back and complete their cutting. In contrast, if one can bring a fat animal as a sacrifice, this is a Mitzvah on Shabbos also. The rule is that the fulfillment of Hidur Mitzvah overrides the prohibition of Melachah on Shabbos, but if one has finished cutting the Tzitzin she'Einam Me'akvin, there is no Hidur Mitzvah to cut them, even on a weekday.
2) Rav Yitzchak Blazer (known as Rav Itzel Peterburger, the Talmid of Rav Yisrael Salanter) in Teshuvos Pri Yitzchak (1:28, page 98, DH Ulam) makes a distinction between starting a new Hidur Mitzvah or merely completing an old Mitzvah. When the Gemara in Menachos 64a says that one should slaughter the fat animal, this means that the Mitzvah he did when he slaughtered the thin animal has been annulled and the latter Mitzvah has been replaced with the new, fat one. One may break Shabbos to do a totally new Hidur Mitzvah. In contrast, cutting the Tzitzin she'Einam Me'akvin is a Hidur Mitzvah, but it is not a new Hidur Mitzvah but rather a completion of the old Mitzvah. On a weekday, it is a Mitzvah to complete this Hidur Mitzvah, but one is not allowed to break Shabbos merely to complete an old Mitzvah.
Kol Tuv,
Dovid Bloom