The Chazon Ish wrote a letter on this subject as follows:
"Halocho matters are established by the Torah, the main part
of which is the Written Torah and its commentary, the Oral
Torah. Even a novi is not allowed to establish a new
interpretation without finding support in the Torah to do so,
and as much as a deficit is an aberration from the Torah, so
too is an addition to the mitzvos of the Torah an
aberration.
"Based on this, one must consult a scholar [i.e. it is an
halachic sheilah — Ed.] on whether or not we are
obligated to keep seven days of mourning for the dreadful
calamities that we have undergone [referring to the terrible
events known as the Holocaust — Ed.]. If we are
obligated, then there is no need for any haskomos. If
we are free of obligation, then we are already warned to hold
by this exemption because the Torah has freed us of any
obligation. Velishmo'a mizevach tov (obedience is more
precious to Hashem than any sacrifice).
"So the proposal to come in, establish and implement, decree
and fulfill is as if treating lightly (hakolas rosh) chas
vecholiloh, the foundation of the halochoh must be wiped
off the agenda before it is even brought up.
"In fact, the establishment of a fast for generations is in
the category of a mitzvah derabbonon. Whatever [fasts
— Ed.] we have today derive from the time when prophecy
still existed. So how can we, this generation, for whom
silence is the best policy, be so insolent as to even
consider establishing matters for generations? Does not the
suggestion itself prove that we are denying the fact of our
sins and our low state, at a time when we are soiled with
sins and transgressions, impoverished, empty of Torah, and
stripped of mitzvos? Let us not overreach ourselves. We
should rather search our ways and do teshuvoh. This is
our obligation, as it is said, `Is this not a fast . . .
etc.' (Yeshayohu 58:6) Sincerely, A. Y. S."
HaRav Y. Z. Soloveitchik (the Brisker Rov) was also consulted
on this subject. A delegation of rabbis came to his home with
the proposal to establish a fast to mark the events of the
Holocaust. The Brisker Rov instantly expressed his total
objection, basing it on what is said during the kinnos
of Tisha B'Av. He referred those present to a kinnah
compiled following the Crusades in the year 4856 (1096)
(beginning "Mi yitein roshi mayim . . . "):
"Take to your hearts now a bitter mourning to bind it, put
on mourning and soil with dust, since their slaughter is
equivalent to the burning of the House of our G-d, the
Ulam and the Biroh, for no moed for the
destruction or conflagration may be added, nor may we move up
mourning but should postpone it. In place of that today, my
cry of woe. I will awaken myself. I will mourn, and I will
bitterly lament."
Rabbi Tzvi Weinman added that HaRav Eliashiv, in his letter
of response to the Admor of Calev (the letter was brought
down in the Kovetz Teshuvos, 18, "To the Admor of
Calev"), relied for his ruling on the Chazon Ish's letter.
The Admor of Calev, who was saved through chasdei
Shomayim from the horrors of the Holocaust, proposed
that: "The whole Jewish people should accept upon themselves
the yoke of Heaven by saying the pesukim pertaining to
ol malchus Shomayim, namely Shema Yisroel,
every day after the tefilloh of Oleinu
leshabei'ach, and they should have the kavonoh to
unite themselves (lehisyacheid) with the six million
martyrs who were sacrificed in the years of the Holocaust,
may the L-rd avenge their blood!"
HaRav Eliashiv answered him in a letter dated the 13th of
Sivan, 5745, 40 years after the teshuvoh of the Chazon
Ish, as follows, showing that the principle of the Chazon Ish
has remained the same to this very day:
"To Kvod Toroso, Honorable Rov, who has seen
affliction and cannot find tranquility for he is unable to
forget the evil that the cursed wicked ones yemach
shemom perpetrated, nor can he take his mind off the
blood of the martyrs which cries out from the ground. The
Honorable Rov has entreated me to give an opinion on the
matter.
"Now we see that when the subject came up, following the
Holocaust, of establishing a public fast for generations for
the destruction of the Jewish people, the Chazon Ish
vehemently opposed it, saying that our generation, a
generation for which silence is the best policy, is not
worthy of establishing matters for generations. As for the
notion of `being united with the martyrs' (lehisyacheid im
hakedoshim) — I know no source for this in
Chazal.
"In my opinion, it is preferable to strengthen what is
already being done by the people of Israel after davening:
to learn mishnayos for the illui neshomos
of those martyrs who left behind them no children or
descendants who could raise up their memory (before the
Master of All). May the Master of Mercy shelter them in the
shelter of His wings for eternity and bring retribution upon
His foes and avenge their blood."