minhagimWe're still mapping where this idea was first discussed. Key passages and related ideas below.
No Haircut Three Weeks (Ashk) / Nine Days (Seph)
During the Three Weeks before Tisha B'Av — the summer fast mourning the Temple's destruction — many Jews avoid haircuts and shaving as outward signs of grief. Ashkenazim (following the Rema) begin from the 17th of Tammuz; many Sephardim (following the Beit Yosef) begin only from Rosh Chodesh Av.
Major Ashkenazi-Sephardic split: Rema from 17 Tammuz, Beit Yosef from Rosh Chodesh Av.
Key passages(3)
Shulchan Arukh, Orach Chayim :: three-weeks-no-haircut :: 551:4↗curated_attribution
Shulchan Arukh, Orach Chayim · Joseph Karo · 1563 CE
High
Shulchan Arukh, Orach Chayim · Joseph Karo · 1563 CE
High
Mishnah Berurah :: three-weeks-no-haircut :: 551:26↗curated_attribution
Mishnah Berurah · Israel Meir Kagan (Chafetz Chaim) · 1875 CE
High