Editing Fast of the Firstborns - Taanit Bechorot

'''Taanit Bechorot''' (Fast of the Firstborns) is a custom from the times of the Geonim for firstborns to fast on the eve of Passover, commemorating the miracle that was performed for them on that night when the firstborns of Israel were saved, while all the Egyptian firstborns were killed that night during the plague of the firstborns.

== Those Obligated to Fast ==
Since the reason for the custom to fast is because they were saved from the plague of the firstborns, in which all firstborns in Egypt died, including those who were firstborn only to their father or only to their mother, the custom was established for generations that not only a halachic firstborn fasts, but anyone who has any aspect of being a firstborn, even if there was a miscarriage before him, or if he is a firstborn only to his father or only to his mother.

When the eve of Passover falls on Shabbat and the fast is moved up to Thursday, even a boy whose Bar Mitzvah falls only on Shabbat is obligated to fast, despite the fact that on the day of the fast itself (two days earlier) he has not yet turned 13 years old.

== Cancellation of the Fast ==
It is a Jewish custom to complete a Talmudic tractate on the eve of Passover, in order to hold a seudas mitzvah (festive meal for a mitzvah), and thereby be exempt from the fast.

Some have the custom not to rely on hearing the completion of a tractate in the synagogue and are stringent to complete a tractate themselves on the eve of Passover.

Some are stringent to complete the fast on the eve of Passover even when they participate in a siyum (completion ceremony).

== With Our Rebbeim ==
The Rebbe Rayatz (Rabbi Yosef Yitzchak Schneersohn) used to complete the fast and not fulfill his obligation by hearing the completion of a tractate, even though he was a doubtful firstborn.

The Rebbe Rashab (Rabbi Shalom DovBer Schneersohn) used to complete a tractate on the eve of Passover, even though he was not a firstborn.

Regarding the Rebbe's (Rabbi Menachem Mendel Schneerson) custom, there are differences of opinion [clarification needed].

== Change in the Time of the Fast ==
If the eve of Passover falls on Shabbat, the Fast of the Firstborns is pushed to the Thursday before, which becomes the established time for the fast. Therefore, a siyum is only held on Thursday (and not also on Friday or Shabbat), and one who did not fast on Thursday should not fast on Friday.

In years when the first day of Passover falls on Shabbat, the Fast of the Firstborns is on Friday, despite the fact that generally one does not fast on the eve of Shabbat.