Mussaf Before Shacharis

Question: I forgot that it was Rosh Chodesh and so arrived late to shul. Should I have davened shacharis while the kehilla were davening mussaf, or davened mussaf with them and davened shacharis afterwards?

Answer: The Shulchan Aruch (OC 286:1) writes that the correct time for mussaf is after shacharis. The Rema adds that if one davened mussaf before shacharis they have still fulfilled their obligation.

The Gemara (Zevachim 90b) discusses which rule takes precedence, that of tadir, the more frequent of two objects takes precedence, or mekudash, the one of greater sanctity. R’ Yitzchak Elchanan Spector (Baer Yitzchak OC 20) argues that if one missed davening shacharis betzibur, they should at-least daven mussaf betzibur and daven shacharis later. While shacharis is an everyday occurrence, and therefore tadir, nonetheless, davening mussaf betzibur is considered mekudash, and so should be performed now, while one can do so with a minyan. While this applies to mussaf on Yom Tov, it does not necessarily apply to mussaf on rosh chodesh and chol hamoed.

R’ Moshe Feinstein (Igros Moshe OC 4:68) disagrees, writing that one must always daven shacharis before mussaf. Firstly, the Torah refers to the korban tamid as haolah, the olah, to emphasise that no korban precedes it (See Mishna Berura 286:5; Kaf Hachaim OC 286:12). Additionally, the rule of tadir means that one must daven shacharis before mussaf. Also, shacharis must be recited in the morning, while musaf can be recited throughout the day.

R' Yitzchak Yaakov Weiss (Minchas Yitzchak 6:36) adds that one who davens the shacharis amida while the tzibbur are davening mussaf may even be considered as davening tefilla betzibbur (See Rivevos Ephraim 8:345).

In conclusion, one who comes late to shul on a day when we daven mussaf must ensure that they daven shacharis first.