Tachanun is not recited in a minyan in which ba’alei simchah (those celebrating a joyous mitzvah celebration) are praying. Therefore, Tachanun is not recited in a minyan in which a chatan (groom) within his seven days of festivity is praying. However, in Shacharit and Minchah before his wedding, Tachanun is recited, although if Minchah is prayed close to the ceremony at the wedding hall, Tachanun is not recited.
Similarly, in a minyan in which one of the ba’alei habrit is praying, Tachanun is not recited. The ba’alei habrit are: the father of the baby being circumcised, the mohel, and the sandak. This exemption lasts from the morning until the celebration meal (seudah); that is, if the brit is held in the morning, Tachanun is not recited in the Shacharit service. If the brit is held after Minchah, Tachanun is omitted in both Shacharit and Minchah (Mishnah Berurah 131:22; and see Piskei Teshuvot 19).
Not only in a minyan in which one of the ba’alei habrit is praying is Tachanun not recited, but even in the synagogue in which the brit is held, Tachanun is not recited. In a building in which there are a number of prayer halls, Tachanun is omitted only in the particular hall in which the brit will be held.
Bar Mitzvah: many are accustomed not to say Tachanun in a minyan in which a youth who is reaching the age of mitzvot on that day is praying, though some do recite it.
Pidyon HaBen: many are accustomed not to recite Tachanun in a minyan in which the father of the son is praying, yet some do.
Likewise, in a prayer service adjoined to the ceremony of a conclusion of a tractate (siyum), or the presentation of a Torah scroll (hachnasat sefer Torah), many are accustomed not to recite Tachanun, though some do.
We already learned that when there is doubt as to whether or not to say Tachanun, the correct way to practice is not to recite it (as brought in halachah 1).
On days of public celebration in memory of prominent Jewish rabbis and righteous people (Yahrtzeit or Hilulah), the opinion of the absolute majority of poskim is that it is necessary to say Tachanun, and that is the custom. The Chassidic poskim maintain that those who follow in the ways of a particular righteous person, engross themselves in his teachings throughout the year, and prepare a feast in his honor on the anniversary of his passing from this world, do not recite Tachanun on that day. However, on the remaining celebration days in memory of other righteous people, Tachanun must be recited.
. Some poskim disagree and maintain that Tachanun is not recited the whole day of the wedding. However, the primary opinion is that it is recited, for many are accustomed to fasting on that day. That is what the Mishnah Berurah 131:21 implies and what Yabia Omer 3:11-12 writes as well.
On the eighth day, as long as seven consecutive 24-hour days have not passed from the wedding ceremony, Tachanun is not recited, as written in Mishnah Berurah 131:26, Yalkut Yosef 131:21, and Piskei Teshuvot 22. However, regarding the recital of sheva berachot, we go according to the days, and someone who got married before sunset already finishes his first day after sunset. This is because with regard to uncertainty concerning berachot, we are lenient (safek berachot l’hakel), whereas concerning the matter of Tachanun, we follow seven full 24-hour days.
. Even if the brit will be conducted at Minchah time, Tachanun is omitted there in Shacharit as well. Additionally, even when there are a number of minyanim for Shacharit, Tachanun is not recited in any of them. (In the past, there was a custom that on the day of a brit, the whole community where the brit was taking place did not recite Tachanun, and perhaps even today it is proper to practice that way in relatively small and close-knit communities, where everyone shares in the joyous occasion.) If the brit is conducted in the morning, some have the minhag to recite Tachanun at Minchah (Piskei Teshuvot 131:17, note 103) and some have the custom not to (Yalkut Yosef 131:27-29).
. See the sources brought by Piskei Teshuvot 131:24 and in the notes there. As a rule, in all the cases of uncertainty mentioned, those who pray in Nusach Sephard (Sephardim and Chassidim) tend not to recite Tachanun, whereas those who pray in Nusach Ashkenaz have more of a tendency to say Tachanun, as is written, for example, in Ishei Yisrael 25:26 concerning pidyon haben.