Shavua tov! Whats the order for someone who misses Shacharit on Shabbat? Does he do the meal without an amida first? Or does he do musaf, meal, and then mincha with shacharis right after? Or does he do meal, mincha, shacharis, musaf? Also how does the order work for Rosh chodesh? I would also please want to know who speaks about this topic, which sefer the answer is found in. Thanks!!

Shalom, Thank you for your question. The question of what to do when someone missed Shacharit is an interesting one. Firstly, there are parts of the morning service that one is obligated to say all day (and not necessarily only in the morning). That being so, you must, before anything else, make sure that you wash your hands (in the ritual 3 times on each hand) and say the blessings over washing, the bathroom, the blessings for learning Torah, and the long list of morning blessings (even if you have missed the morning and it is now afternoon). Next, it will depend on what time of day it is that a person is now able to pray. If it is before halachic midday (that is halfway between sunrise and sunset – usually not at 12 o’clock), then one should pray all the morning service before eating a meal. [Some opinions say that if it is late in the morning [after the 4th hour of the day] than one is not allowed to say the blessings before and after the Shema – but if a person is praying at this time for good reason, they may say even these blessings]. He should then pray Musaf and then make kiddush and then eat the meal. If it is already half an hour after halachic midday, then one should say Shema (without the blessings), and then say Mincha. If one missed Shacharit for a good reason (they were ill, etc), then they should say the Amidah of Mincha again as a make-up prayer for the Shacharit they missed. (If one missed Shacharit out of laziness, then it is not so clear they get to use a make-up prayer). Then Musaf should be said. Even though we normally say Musaf before Mincha, in this case, as the time for Mincha has arrived, it takes precedence (this rule is sometimes not followed when a whole community is davening Mincha late, but only for individuals). After all this, one should make kiddush and have their meal. The same rules apply for Rosh Chodesh. As to where to learn this – one could begin with the Kitzur Shulchan Aruch (Concise Code of Jewish Law) by Rav Gansfried zt”l. Chapter 21. Blessings.