This Halacha is an excerpt from our Sefer
Wearing Shabbos clothing on Shabbos and by a Bris:
Some Poskim rule it is forbidden to wear Shabbos clothing on Shabbos Chazon, with exception to wearing a Kesones [Shabbos undershirt] which is allowed, [and so was the old custom of Ashkenaz]. Other Poskim however rule that on Shabbos of the nine days, including Shabbos Chazon, one is to wear his regular Shabbos clothing [and so is the Sephardic custom]. [Practically, the widespread custom today amongst all Jewry [Sephardim Chassidim, as well as almost all communities of Ashkenazi Jewry] is to wear all one’s regular Shabbos clothing on Shabbos Chazon.]
Paroches: The Paroches for Shabbos is placed in Shul as usual. This is with exception to when Tisha B’av coincides with Shabbos and is differed to Sunday, in which case the Shabbos Paroches is not placed. [However, the widespread custom is to place the Shabbos Paroches even at this time.]
Shabbos clothing during a Bris: When a Bris is taking place during the nine days it is accustomed that the father [and mother] of the child, the Mohel and the Sandek [and grandparents] to wear Shabbos clothing. [Furthermore, the custom is for also other close relatives to wear Shabbos clothing.]
May one wear Shabbos clothing by a Pidyon Haben or Bar Mitzvah?
Yes. The relatives and Baalei Hasimcha that normally wear Shabbos clothing by the event may do so by a Bar Mitzvah and Pidyon Haben.
May one wear new Shabbos clothing on Shabbos?
No [unless he has no other clothing available at all].
May a Baal Bris wear new clothing?
No, as stated above.
 Rama in 551:1; M”A 551:4; Elya Raba 551:39; Teshuvos Rashal 27; Mateh Moshe 736; Mordechai Tisha B’av; Hagahos Ashri; Aguda; Rokeiach; Custom of Chasam Sofer, brought in Likkutei Chaver Ben Chaim
 M”A 551:4 in name of Mateh Moshe “is only worn due to sweat”; 559:10; Kneses Hagedola 551; See Kaf Hachaim 551:12 in name of Hagahos Mordechai who says a Kesones is a coat.
Linen clothing and the Shabbos before Shabbos Chazon according to Rama: One may wear Shabbos clothing made of linen. [Rama 551:3] This implies that one may wear all Shabbos clothing made of linen and seemingly contradicts the previous ruling. The Kaf Hachaim 551:64 explains that in 551:1 the Rama referred to Shabbos Chazon while in 551:3 he is referring to the Shabbos before Shabbos Chazon.
 Beis Yosef 552; Arizal; Radbaz 2:693; Chacham Tzevi as brought in Siddur Yaavetz p. 68; Machazik Bracha 551:4; Chayeh Adam 133:21 that so is custom of Vilna based on ruling of Gr”a; M”B 551:6 in name of Gra and Chacham Tzevi; Aruch Hashulchan 551:11; Kaf Hachaim 551:13; Divrei Nechemia Y.D. 333-27 that so was custom of Admur; Likkutei Maharich; Nimukei Orach Chaim; Sefer Haminhagim p. 93 [English] that so is our custom and in footnote 359 that so was custom of Alter Rebbe; Toras Menachem 44:172 that so was custom of Admur
 As rules Beis Yosef ibid that Sefaradim never accepted this custom; Kaf Hachaim 551:13
 Divrei Nechemia ibid and Sefer Haminhagim p. 93 [English]
 As testifies the Aruch Hashulchan ibid; As was Minhag of Gr”a, and town of Vilna, as ruled the Ashkenazi Poskim brought in previous footnotes; See Moadim Uzmanim 5:343; 7:256
 Rama 551:3 “One spreads white clothes as usual like by other Shabbosim”; M”B 551:7;
 M”B 551:33
 Rama 551:1
 Rama 551:1
 Piskeiy Teshuvos 551:4 based on our Minhag to wear Shabbos clothing
 Michaber 551:1
 Chayeh Adam 133:21; Kitzur SHU”A 122:15; Kaf Hachaim 551:7
 Shaareiy Teshuvah 551:1
 Shaareiy Teshuvah 551:1; Ashel Avraham Butchach Tinyana 551
 Piskeiy Teshuvos 551:3; Nitei Gavriel 15:22
 M”A 551:21; Elya Raba 551:40; M”B 551:9; Kaf Hachaim 551:16; See also Zera Emes 76; Machazik Bracha 551:3; Zechor Leavraham 551:9; Shaareiy Teshuvah 551:1; Kaf Hachaim 551:9