Seder HaTephilah…Nusach Ha’Ari [prayers for Sabbath and Festivals]. With commentary by R. Shneur Zalman of Liadi.

This important Siddur is known in Chabad circles as the Siddur D”ach (Divrei Elokim Chaim), as opposed to other Chassidic Siddurim that do not contain Chabad Kavanoth (meditations). It would have been used by the “Ovdim” of Chabad those select few who would piously pray for several hours, with intense contemplative devotion.