R. Yitchak Al-fasi (1013 – 1103) lived in North
Africa and Spain during the Golden Age of Qaraism. It is quite natural that we
find many instances of anti-Qaraite legislation in his writings.

Below are four such cases:

1) R. Al-fasi had the shofar blown on Shabbos
Rosh HaShanah in his beth din in Fez, Morocco. (See
discussion here: here). This
ruling and practice baffled many later authorities as it seems to contradict
the Talmud Rosh HaShanna 29b. R. Zerachiah Ha-Levi wrote about R. Al-fasi’s
opinion – וזה אחד מן המקומות המתמיהים הנמצאים בהלכות  (המאור הקטן ר”ה פ”ד).

When we consider that the Qaraites (of whom existed a large community in Fez)
did not blow a shofar at all on this holiday because such blowing is not
clearly written in the Torah, it is understandable why R. Al-fasi would desire
to have shofar blowing take place. Refraining from blowing the shofar would be
like surrendering to Qaraite views. We should also recall that Rosh HaShanah
can fall out on Shabbos as often as five times in ten years.

Aaron ben Elijah (1328-1369), a prominent
Qaraite theologian wrote:

Read more on the Qaraite halacha here

2) R. Al-fasi was a key player in the
transition of the evening prayer from reshut to chova:

Summary: Since the close of the Talmud, the
accepted halacha had been תפילת ערבית רשות.
Towards the end of the tenth century the custom solidified amongst Qaraites to
pray only twice a day. To create a social divide, Rabbanite authorities
responded by requiring every Rabbanite follower to pray three times each day.
By attending synagogue three times a day one affirmed his allegiance to the
Rabbanite camp; also by praying more often than Qaraites, Rabbanites
distinguished themselves as being more holy and religious. The Franco-German
sages, distant from the Qaraite-Rabbanite scene, upheld the original halacha of
תפילת ערבית רשות.

Explanation: All early Gaonim ruled aravit
is optional (עיין בראשונים ברכות פרק תפלת השחר).
In early Qaraite times there were different views as to how many times a day
one should pray. Anan ben David, the early sectarian schismatic, believed that
only two prayers should be said: “Anan rejected the maariv – service, as being
only a Rabbinic innovation (See Brochos 27b), and prescribed two daily services
only in accordance with the times on which the Temidim were sacrificed” (Jacob
Mann, “Anan’s Liturgy and his half-yearly cycle of the reading of the law”, Karaite
Studies (1971) edited by Philip Birnbaum pg. 285). R. Saadya Gaon
(882- 942), who had many interactions with Ananites, responded by requiring
Rabbanites to pray three times- he made maariv mandatory (chova).

This was only the opinion of the Ananites;
other sectarian Qaraite-like groups had other views as to the number of daily prayers
required. Later, in the mid-tenth century, R. Sherira Gaon (906-1006)
maintained the early gaonic psak that maariv
is reshut, but
wrote that one who does not daven maariv is a “poretz
geder” (here).

Late in R. Sherira’s lifetime and in subsequent
years, the view among Qaraites was solidifying that only two daily prayers were
required. The Qaraite scholar, Levi ben Yefet, writes in his Sefer
ha-Miswot (latter half of the 10th century),II pp.  501-502:

הדבור
בכמה זה השער- כבר נתחלפו בו ואשר עליו ההמון, כי הנה שתי תפלת בכל יום בקר וערב
שנאמר “ולעמוד בבקר בבקר להודות ולהלל ליוי וכן לערב”,… אשר יהיה זולת אלה הוא
נדבה…

ואמרו
מקצת חכמים כי חובה גם היא…ואלה הג’ תפלותיהם אשר זכר אותם דוד ע”ה “ערב ובקר
וצהרים אשיחה…” …. והקרוב עמי כי אלה הכתובים לא יורו על חיובה…

Shortly thereafter, R. Al-fasi (1013 – 1103)
further enforced the tri-daily prayer system by stating “והאידנא
נהוג עלמא לשוייה כחובה”. A Jew who belonged to the Rabbanite camp
distinguished himself from the Qaraites by attending synagogue three times a
day. I am preparing a lengthy paper on this topic – “The Transition of Aravit
from Reshut to Hova–
a Rabbanite Response to Qaraism”.

3) R. Al-fasi participated in the anti-Qaraite
transition of minor fast days from being voluntary to mandatory.

Though the Gaonim and R. Chananel (990-1053)
explicitly say that not eating on the three minor fast days is the individual’s
choice (as per the Talmud’s ruling RH 18b- אין שמד ואין
שלום – רצו – מתענין, רצו – אין מתענין), R. Al-fasi chose to overlook this detail
about fast days in his halachic writings. The purpose of this intentional
omission was almost certainly to separate Rabbanites from the Qaraite community
who did not observe the Rabbanite fasting calendar.

Briefly, here is the sugya
in Rosh HaShannah 18b:

אמר ר”ש
חסידא מאי דכתיב (זכריה ח) כה אמר ה’ צבאות צום הרביעי וצום החמישי וצום השביעי
וצום העשירי יהיה לבית יהודה לששון ולשמחה קרי להו צום וקרי להו ששון ושמחה בזמן
שיש שלום יהיו לששון ולשמחה אין שלום צום אמר רב פפא הכי קאמר בזמן שיש שלום יהיו
לששון ולשמחה, יש (גזרת המלכות) שמד צום, אין (גזרת המלכות) שמד ואין שלום רצו
מתענין רצו אין מתענין אי הכי ט”ב נמי אמר רב פפא שאני ט’ באב
הואיל והוכפלו בו צרות

The Gaonim:

– בזמן
הזה, בדורות הללו, שאין שמד ולא שלום, רצו מתענין לא רצו אין מתענין…. הילכך שלושת
צומות, מי שאינו
רוצה לצום אין בכך כלום ואינו מחוייב בהן. (תשובות הגאונים גנזי
קדם ח”ג עמ’ 43)

R. Chananel:

שיש שלום
– כלומר כל זמן שבית המקדש קיים יהיה לששון ולשמחה. יש שמד – צום.  אין שמד
ואין שלום –  כגון עתה בזמן הזה, רצו מתענין רצו אין מתענין. וכיון שאם רצו
שלא להתענות בהן אין חובה עליהן, לפיכך אין שלוחין יוצאין בהן.
(רבינו חננאל – ראש השנה יח, ב)

הרב
ברג’לוני ז”ל כתב מ”ט קבעום האידנא חובה? מפני שהם דברי קבלה … (שערי תשובה
סימן עז)

By the time of Ramban (1194–c. 1270) and later
authorities mandatory fasting was well established in Spain. (Rashba, though,
is an exception- he still considered the fasts optional.)

About the practice of the Qaraites, Levi ben
Yefet, writes in his Sefer ha-Miswot (latter half of the
10th century),III pg 452: Levi be writes

הדבור בצומות אשר יצומו אותם הרבנים … והוא יום
יז’ בתמוז ויום ט’ באב, ויום עשרה בטבת… ואולם לא נצום אותם עמהם…

Dr. Isaac Gottlieb summarizes (here):

The Karaite calendar does not take note of our
holidays of Hanukkah, Tu-b’Shvat… because these days are not mentioned in the
written Torah. Three of the four fast days associated with the destruction of
the First Temple are observed in Karaite tradition, but on different days from
us: the “fast of the fourth month,” which we observe on the 17th of Tamuz, they
mark on the 9th of Tamuz (cf. II Kings 25:3-4); instead of the Ninth of Av the
Karaites fast on the 7th and the 10th of Av (II Kings 25:8; Jer. 52:12-13);
instead of the Fast of Gedaliah, which we observe on the 3rd of Tishre, the
Karaites fast on the 24th of Tishre (Neh. 9:1). The fast on the 10th of Tevet
is the only one which they observe on the same date (Jer. 52:4-5). They do not
observe the Fast of Esther but celebrate Purim for two days, and on leap years
they only observe it in the first month of Adar.

Rabbi David Bar-Hayim’s view is that the
transformation from optional to mandatory fasting occurred because later
rishonim believed they lived in time of שמד
– hence fasting was obligatory. More recent authorities only cited the words of
these late rishonim and that perspective became the norm. Here is his
discussion of this topic: “The Four
Fasts and their Halakhic Status Today”. Rabbi Bar-Hayim suggests that the situation
today (the political climate – war vs. peace) is not different than that of the
Gaonim and R. Chananel – אין שמד ואין שלום. 
This assessment has practical halachic implications. I suspect, though, that
the transformation was not only because of ‘wartimes versus peaceful times’ but
was also political and anti-Qaraite.

Rambam also omits this Talmudic leniency of רצו מתענין רצו אין מתענין. The Halachot
digest of R. Al-fasi and Mishnah Torah of Rambam were both intended
to replace Talmud study for the lay population. By ignoring the leniency of
permissibility of skipping the minor fasts, these sages made sure their general
readers would assume fasting is obligatory- thereby segregating them from the
Qaraite communities who did not fast on Rabbanite fast days.

The language used by R. Y Barzillai, “קבעום האידנא חובה”, is similar to that employed by R.
Yitzchak Al-fasi and others – “והאידנא נהוג עלמא לשוייה
כחובה” – in explaining why, in the eleventh century, Jews were
required to pray the evening prayer every night (עיין
ברכות פרק תפלת השחר). This may hint at the same reason for
change- to separate Rabbanites from Qaraites. See Case#2.

Furthermore, Sma”k 96 (R. Yitchak Corbeil- 13th
century France) and Kolbo Laws of Taanith (Provence
14th century) cite the Gemara רצו מתענין רצו אין מתענין
. These authors only cite practical matters- it is clear they still considered
the minor fasts optional. The great R. Tam was asked if a pregnant woman needs
to fast on the minor fasts. He responded by citing the Talmud – that these
fasts are optional (cited in Hagaath Maimoni Laws of Taanith 5).

These European sages lived far from Qaraites and therefore had no need to
respond to sectarian practices.

My suggestion – that the transformation of the
three minor fasts from being optional to mandatory was a reaction to Qaraism –
is novel and requires some more investigation and research…והמשך יבוא.

4) R. Yitchak Al-fasi, and his teacher, R.
Chananel, created a six hour waiting requirement between meat and dairy in the
early eleventh century – thereby limiting the social participation of
Rabbanites with Qaraites. This was not the common practice in Judaism until
their new legislation. I elaborated on this in “Waiting Six Hours for Dairy- A
Rabbanite Response to Qaraism” –  here.