Eve of Passover on Shabbat
When the Eve of Passover (Hebrew: ערב פסח, Erev Pesach) falls on Shabbat, special laws apply that are not followed when the Eve of Passover occurs on any other day of the week, and various adjustments are made in the preparations for the holiday from the usual routine.
The Eve of Passover occurring on Shabbat is a relatively rare occurrence, falling on Shabbat less often than any other day of the week it possibly can. Other days of the week on which the Eve of Passover can occur include Monday, Wednesday, and Friday.
While an Eve of Passover on Shabbat sometimes occurs as many as three times in a decade, other times, as many as 20 years will pass between two occurrences. During the 20th century, the Eve of Passover fell on Shabbat in 1903, 1910, 1923, 1927, 1930, 1950, 1954, 1974, 1977, 1981 and 1994. In the 21st century, the Eve of Passover has came out on Shabbat three times: in 2001, 2005, and 2008. Future occurrences in the 21st century will take place in 2021, 2025, 2045, 2048, 2052, 2072, 2075, 2079, and 2099.
Fast of the Firstborn
When the Eve of Passover falls on Shabbat, the Fast of the Firstborn customarily takes place on the Thursday. This is because it is forbidden to fast on Shabbat (except when Yom Kippur falls on Shabbat), and it is preferable not to hold a fast on Friday. Though it is normally forbidden to eat starting from nightfall before conducting the Search for Chametz, according to the Mateh Moshe and Maharil, a firstborn who is fatigued or uncomfortable from the fast may eat some food before the search, or else another person may be appointed to perform the search on behalf of the firstborn.
Rabbi Moshe Feinstein (OC 4:69:4) writes, based on the Rema (who is supported by a similar ruling of Rabbi Joseph ben Meir Teomim in his P'ri M'gadim), that one who breaks the adjusted Thursday fast might be required to fast on Friday. Since there are many opinions that dispute the Rema (such as the Shulchan Aruch, Turei Zahav, Eliyah Rabba, Chayei Adam, Sh'vut Ya'akov, Mor U-K'tzi'a), Rabbi Feinstein writes that, practically speaking, one should not fast on Friday in such circumstances. This rationale may be based on the Korban N'tan'el, who writes that excessive strictures regarding keeping the Fast of the Firstborn should not come at the expense of possibly fasting unnecessarily during the month of Nisan.
The above halakhic quandary is avoided completely if a firstborn fasts the entire day on Thursday. However, Rabbi Feinstein makes no mention of this requirement. In order for a firstborn (who eats on Thursday) to comply with the ruling of the Rema, the Piskei T'shuvot suggests participating in a second siyum on Friday, while Rabbi Tzvi Pesach Frank suggests partaking on Friday of leftovers from the previous day's siyum.
The Search for Chametz
Normally, the Search for Chametz (leavened bread) occurs on the night of the 14th of Nisan, which is one night before the start of Passover. But when this night occurs on a Friday night, since use of a candle, and the act of burning chametz are forbidden on Shabbat, the Search for Chametz takes place one night earlier on the 13th.
Chametz is burned on the following Friday morning. However, consumption of chametz is permitted throughout this day.
During Shabbat, when there is a mitzvah to eat three meals consisting of bread, three meals are likewise consumed on this day. But since the restriction on consuming chametz begins on Saturday morning (usually some time between 9:30 and 10:00 a.m.), the three meals must be completed by the deadline, which will vary in each year.
For the Shabbat that coincides with the Eve of Passover, enough bread will be kept in the household in order to complete these three meals. It'll be stored in a location where it does not come in contact with Passover food or dishes.
The first meal is consumed on Friday evening as usual. On Saturday morning, morning services at synagogue are held earlier than usual. Following services, a second meal is held and finished quickly. After an interruption, a third meal is begun in which the remainder of the chametz is consumed by the deadline.
While matzah can ordinarily be used to fulfill the obligation of Shalosh Seudot on Shabbat, it is not used for any of the three meals on the Eve of Passover due to a restriction forbidding consumption of matzah on this day.
Remainder of year
In years in which Passover fall on the Eve of Shabbat, some unusual effects take place in regards to other Jewish holidays at other times of year.
For example, Purim will fall on Friday, necessitating adjustments in the regular schedule of events for Purim.
In years when the Eve of Passover is on Friday and the first day of Passover is on Shabbat (a more common occurrence), the ninth day of Av will fall on Saturday, and since fasts other than Yom Kippur are not observed on Shabbat, Tisha B'Av will be postponed to the following Sunday, which is the tenth of Av. But in this rare years, Tisha B'Av is observed on the actual ninth day of Av on a Sunday, and there is no "week in which Tisha B'Av occurs" as a level of mourning prior to the start of Tisha B'Av.
- Halachos of Erev Pesach Which Occurs on Shabbos by Rabbi J. David Bleich, a publication of Yeshiva University