Siddur Torah Ohr al-pi Nusach Ha'Ari z”l.

The Sha’ar HaKollel is an invaluable appendix to the Siddur of R. Shneur Zalman of Liadi. It explores the halachic rulings and customs established by the Alter Rebbe in his Siddur and explanations why they differ at times from the rulings in his Shulchan Aruch. A student of the Tzemach Tzedek, R. Avraham Dovid Lavut, served for forty years as rabbi of Nikolayev, Russia - the birthplace of his illustrious great-grandson, R. Menachem Mendel Schneerson, the last Rebbe of Lubavitch. See M.M. Laufer, Yemei Melech (1991) pp. 39-55.