Chapter 122:2
Between the 17th of Tammuz and Tisha B'av
2. It is customary not to recite the blessing "Shehecheyanu" (1) during
these days [between the 17th of Tammuz and the 9th of Av] (2). Therefore,
one should not buy or wear a new garment that would require one to recite
this blessing. At a "Pidyon Haben" (3), however, [the father] does recite
the blessing "Shehecheyanu," so as not to postpone the fulfillment of the
mitzvah.
One may show leniency and recite this blessing over a new fruit on Shabbos
or even during the week (4), if it will be impossible to find this fruit
after Tish'ah B'av (5).
[Teachers and parents] should not strike their students or children during
these days.
FOOTNOTES:
(1) The translation of this blessing is: "Blessed are You, Hashem, our
L-rd, King of the universe, Who has kept us alive, sustained us, and
brought us to this time."
It is recited upon: a) eating seasonal fruits of a new season for the first
time that year b) purchasing a new garment of significant value to the
wearer (e.g., a new suit or dress) c) performance of a time-dependant
mitzvah or d) deriving significant benefit from an event.
(2) Although a person in mourning over the loss of a close relative is
permitted to recite this blessing, nevertheless, since the three weeks
between the 17th of Tammuz and the 9th of Av is a season set aside for
punishment ("zman puranus"), it would not be appropriate to bless G-d for
having "brought us to this time." (Mishna Berura 551:98).
The Vilna Gaon argues that this custom of not reciting "Shehecheyanu" is an
unnecessary stringency, and the Taz also has doubts about it. Therefore,
the custom is to be lenient and allow the recitation of the blessing on
Shabbos (Ibid.)
(3) A "Pidyon Haben" is the ceremony of the redemption of a first-born
male, which takes place 30 days after the birth.
(4) If the fruit can be preserved until Shabbos without becoming rotten, it
is best to do so (Ibid. 101).
(5) A pregnant woman or a person who is ill, may eat new fruit without the
"shehecheyanu" blessing (Ibid. 99).