The founder of Chabad Hasidism, Rabbi Shneur Zalman of Liadi (1745-1812), passed away on the night of the 24th of Tevet, at approximately 10:30 PM, after reciting the Havdalah prayer, which marks the end of Shabbat. He is also known as the Alter Rebbe, author of the Shulchan Aruch and the Tanya.
The Rebbe was in the village of Peyena, escaping from Napoleon's army which, three months earlier, had razed the Rebbe's village on its advance towards Moscow.
He was 68 years old and was succeeded by his son, Rabbi DovBer of Lubavitch.
Kabbalah explains that on the day a Tzaddik—a righteous person—passes away, all the spiritual work they did throughout their life is revealed more powerfully on Earth. That is why this is a special day.
Among the customs practiced on the day of a Yahrzeit - anniversary of death - is the study of the chapters of the Mishnah that begin with the letters of the deceased's name, since the word Mishnah (which refers to the compendium of Jewish laws, compiled in the year 200 CE by Rabbi Yehuda HaNasi) has the same letters as the word Neshamah - soul, indicating that its study has a positive effect directly related to the soul of the Jew.
Author of the Shulchan Aruch?
The Shulchan Aruch was written by Rabbi Yosef Karo (Safed, 1565).
Hi Jorge, the Alter Rebbe composed a more modern version of the Shulchan Aruch at the request of the Maggid of Mezritch. This version has the advantage of including the halakha along with its rationale. Furthermore, being more modern, it includes information that Yosef Karo did not have (more rishonim, acharonim, etc.).
The book is known as "Shulchan Aruch HaRav," the Rabbi's Code of Jewish Law. The entire Jewish world knows and recognizes the Alter Rebbe as "The Rav." Unfortunately, the vast majority of the book was burned, and only the following parts remain:
1) Orach Chaim, from the beginning to the laws of blessings over food. Almost complete laws of Shabbat, laws of Pesach, part of Sukkot, laws of Yom Tov, Rosh Hashanah and Yom Kippur complete, laws of Torah Study.
2) Iore Dea, a little bit of Shjitá laws, Nida laws
3) Joshen Mishpat, laws of body care and damages, laws of Interests.
The laws of Shabbat, in particular, are widely studied in the Jewish world for their clarity and depth. Every halakhic authority specializing in Shabbat must study this part of the Shulchan Aruch of the Alter Rebbe.
There are other additional writings, such as notes in the Siddur, two versions of a summary of laws of blessings (for food and others), some halakhic responsas, plus a vast literature on Hasidic philosophy, where, sometimes, certain halakhic matters appear from which one extracts what the Alter Rebbe thinks about those subjects.
To that must be added testimonies passed down from generation to generation, almost always by Chabad Rebeim, regarding the different Chabad customs in Jewish life which, despite not being written in the Alter Rebbe's Shulchan Aruch, are known to be true. Furthermore, there are certain specific matters that the Alter Rebbe writes about in his Shulchan Aruch that, according to the testimonies of Rebeim and Hasidim, are not practiced in that way in Chabad, but rather in another...
In any case, that is the matter of the Shulchan Aruch of the Alter Rebbe.
Greetings!