2098 —המנהג שלא לגלח שערות הבן עד גיל שלש

B"H, 6 Iyar, 5713.

Brooklyn.

Haraha"ch vavac"h iy"a nu"n etc. Yerachmiel Gradman

Shalom u'Vrachah!

Regarding what you wrote about the custom of not cutting a boy's hair until he turns three years old: You will find this at the end of Seventy Tamarim (where it concludes that a child's first haircut is a mitzvah-education act, as also stated in Ba'er Heitev and Shaarei Teshuvah on Shulchan Aruch Yoreh Deah 131). This is also brought in the Siddur of Maharid, grandson of the tzt"z (and there he also explains these matters according to Chassidus). I have also heard several times from my father-in-law, the Rebbe—below is an excerpt from his letter regarding how to conduct oneself then.

Therefore, it is very appropriate that you too observe this. It is already well known that the ruling is: Minhag Yisrael Torah hi (the custom of Israel is Torah). See also Rambam at the beginning of Hilchos Mamrim, where it appears that a custom accepted by all Israel enters into the category of positive and negative Torah commandments. See Choshen Mishpat siman 365 and Be'urim se'if katan 22; Hilchos Talmud Torah by the Alter Rebbe at the beginning of chapter 2. In Sefer Keter Shem Tov (by Rabbi Gagin), page 591, it says that in Eretz Yisrael they do this when the boy turns four! Perhaps this is a scribal error and it should say three years.

With blessing, awaiting good news.

Summary

The Rebbe writes that not cutting a boy's hair until age three is an established Jewish custom with deep halachic and chassidic roots. He encourages maintaining this practice as part of Jewish tradition and education.