Translation:Shulchan Aruch/Orach Chaim/286

Laws of Musaf on Shabbat
1. The Laws Pertaining to the Mussaf Prayers on Shabbat, 5 Seifim: The time for the Mussaf prayer is immediately after the prayer of dawn (Shacharit) and one may not delay it (Mussaf) past the end of the first seven hours of the day. And if one prayed it after the seven hours he is called a sinner even though he fulfilled his obligation since its time is all day. And if one forgot and did not pray past its entire time, it (Mussaf) does not have tashlumin (another prayer to make up for it). And (Mussaf) has the raising of the hands (Birkat Kohanim). ''RAMA: And if one prayed it before the Shacharit prayer he fulfilled his obligation. (Ohel Moed in the name of the Rashba; the R"i, perek Tefilot HaShachar)''

2. Every individual is obligated to pray the mussaf prayer, regardless of whether there is a congregation in the city or not. ''RAMA: And afterwards, the shaliach tzibbur repeats the prayer similar to the rest of the prayers. [Beit Yosef in the name of Shibolei Leket]''

3. It is permitted to eat lightly after the Morning Service before the Mussaf Service, such as partaking of fruits, or even bread, even to the extent that one sates his heart. But it is forbidden to eat a meal.

4. If the person had the option of reciting two prayer services, the Afternoon Service and the Mussaf Service, e.g., he delayed the recitation of the Mussaf Service until the time for the Afternoon Service and six and a half [seasonal] hours [after sunrise] (Tur) – arrived, he must recite the Afternoon Service first and Mussaf afterwards. ''RAMA: But if one begins with Mussaf he has fulfilled his obligation. [Beis Yosef in the name of the Rashba].'' And there are those who say that this is specifically if he has to pray both of them right now, like in a situation where he wants to eat and it is forbidden for him to eat until he prays Minchah; in this situation he can begin with Mussaf. ''RAMA: This is if the time for Minchah Ketanah has arrived, he may daven Minchah during (this time). (R"il the Rosh in the name of the Yerushalmi).'' There are those who hold that this should not be done in a congregation, i.e. to begin Minchah before Mussaf, in order that people not err.

5. On Shabbat and Yom Tov one does not say 'Barchu' after the end Kaddish (and see above Siman 133).