6. Bris Mila during the Nine days:

Shabbos clothing during a Bris:[1] When a Bris is taking place during the nine days it is accustomed that the father [and mother[2]] of the child, the Mohel and the Sandek [and grandparents[3]] to wear Shabbos clothing. [Furthermore, the custom is for also other close relatives to wear Shabbos clothing.[4]]

Meat and wine:[5] One may eat meat and drink wine[6] during a Bris Mila Seudas Mitzvah which is taking place during the nine days.[7] However, only those who are coming to the meal out of respect for the Baal Hasimcha, or other similar reason, are allowed to eat.[8] However, those joining simply to be allowed to eat meat and drink wine are forbidden to eat meat and wine.[9]

The week of Tisha B’av:[10] Within the week of the Tisha B’av, only ten people, [in addition to relatives[11]], are to eat meat or drink wine during the meal.

Erev Tisha B’av:[12] The above allowance to eat meat and drink wine during a Seudas Mitzvah applies even on Erev Tisha B’av, with exception to the Seudas Hamafsekes. [When having the meal on Erev Tisha B’av, it is proper to eat it in the morning.[13]]

Kos Shel Bracha:[14]  One may say Birchas Hamazon over wine [i.e. Kos Shel Bracha] by a Seudas Mitzvah.

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[1] Michaber 551:1

[2] Chayeh Adam 133:21; Kitzur SHU”A 122:15; Kaf Hachaim 551:7

[3] Shaareiy Teshuvah 551:1

[4] Shaareiy Teshuvah 551:1; Ashel Avraham Butchach Tinyana 551

[5] Rama 551:10

[6] See Pesakim Uteshuvos 265:15 regarding drinking the wine

[7] The reason: As the Sages never decreed that one not eat meat and wine by a Seudas Mitzvah during the nine days. [Mateh Yehuda ibid; Kaf Hachaim 551:138]

[8] Rama ibid “All those which are affiliated with the meal”

[9] M”A 551:35; Taz 551:12; Drashos Maharil; M”B 551:76 based on Rama ibid “but not anymore than this amount”; Kaf Hachaim 551:163

[10] Rama ibid

[11] M”A 551:35; Taz 551:12; M”B 551:77

[12] Rama ibid

[13] M”A 551:37; M”B 551:78

[14] M”B 551:71