Mussaf (also spelled Musaf or Musof) is an additional service that is recited on Shabbat, Yom Tov, Chol Hamoed, and Rosh Chodesh. The service, which is traditionally combined with the Shacharit in synagogues, is considered to be additional to the regular services of Shacharit, Mincha, and Maariv. In contemporary Hebrew, the word may also signify a newspaper supplement.
During the days of the Holy Temple, additional offerings were offered on these festive days. Mussaf is now recited in lieu of these offerings.
Mussaf refers to both the full service (which includes the Amidah and all Jewish prayers that follow that are normally recited during Shacharit) and the Amidah itself that is recited for Mussaf. The main addition is a fourth blessing of the Amidah specially for these days. The correct time to recite musaf is until the seventh Halachic hour of the day (when the day is divided up into twelve-hour parts); however, it is proper to begin musaf before 6.5 relative hours, because after this time there is a doubt as to whether Musaf of Mincha should be recited first. If one did not recite it by this time, it is permissible to recite it for the remainder of the day; one who deliberately does this is called a "sinner".[1] Traditionally, it is recited immediately following Shacharit as a combined service.[2]
The Priestly Blessing is said during the Reader's repetition of the Amidah. In the Eastern Ashkenazic rite outside the land of Israel, the Mussaf Amidah of major Jewish holidays is the only time the Priestly Blessing is said.