Omer gyásza: zenehallgatás, 33 nap

With regard to the twelve thousand pairs of Rabbi Akiva’s students, the Gemara adds: It is taught that all of them died in the period from Passover until Shavuot. Rav Ḥama bar Abba said, and some say it was Rabbi Ḥiyya bar Avin: They all died a bad death. The Gemara inquires: What is it that is called a bad death? Rav Naḥman said: Diphtheria.

It is customary not to cut one's hair until Lag BaOmer, since it is said that that is when they stopped dying. One should not cut one's hair until the 34th day, in the morning, unless the 33rd day falls on Friday, in which case one may cut one's hair then, in honor of the Sabbath ("kavod Shabbat"). Rema: But in these countries, we do not follow the custom he advocates; rather, we cut our hair on the 33rd day, and we rejoice a bit, and we do not say Tachanun (Maharil and Minhagim). And one should only cut one's hair on the 33rd day itself, but not on its evening. However, if it falls on Sunday, our custom is to cut our hair on Friday in honor of the Sabbath (Maharil). Someone who is performing a brit milah (i.e., the sandak, mohel and the infant's father), or circumcizing his son, is allowed to cut his hair during sefirah in honor of the circumcision (Hagahot Minhagim).

It is customary not to get married between Pesach and Shavuot, until Lag BaOmer (the 33rd day), because during that time, the students of Rabbi Akiva died. However, to do "erusin" and "kiddushin" (engagement and betrothal) is OK. And even for "nisuin" (marriage), if someone did so, we do not punish him. Rema: however, from Lag Ba'Omer onwards, all this is permitted (Abudraham, Beit Yosef & Minhagim).

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