Isru chag
Isru Chag (Hebrew: אסרו חג, lit. 'Bind [the] Festival') refers to the day after each of the Three Pilgrimage Festivals in Judaism: Passover, Shavuot and Sukkot. The phrase originates from the verse in Psalms 118:27, which states, "Bind the festival offering with cords to the corners of the altar." According to the Talmud: With regard to anyone who establishes an addition [issur] to the Festival on the day after the Festival by eating and drinking, the verse ascribes him credit as though he built an altar and sacrificed an offering upon it, as it is stated: “Add [isru] to the Festival with fattened animals [ba’avotim] until the horns of the altar.” In a responsum to a community that had inquired as to the rationale behind the observance of Isru Chag, Yosef Hayyim (1832–1909) cited Isaac Luria (1534–1572), the founder of Lurianic Kabbalah, to the effect that Jews connect the day after the holiday to the holiday itself due to the remaining “light” of the holiday: in other words, so that the sanctity of the holiday will be extended.