On a day when mussaf is recited, an individual for some reason must daven mussaf later on in the day rather at the standard time within the shacharis service. Should this later mussaf be accompanied with Ashrei before and aleinu afterwards, or should it be recited on it’s own?
Answer:
There is not obligation to open the Mussaf prayer with Ashrei, but it is worthy practice. There is no need to say Aleinu afterwards.
The Ashrei that we recite before davening is in order to introduce our prayer with praise of Hashem. The Mishnah Berurah writes that this is not an obligation, but worthy practice, and therefore where there is a good reason, Ashrei can be skipped (see 234:6; 108:14; Or Le-Zion Vol. 2, 15:3).
There is certainly no obligation to precede the extra Mussaf prayer with Ashrei, for there is no enactment of any kind to recite it. Nonetheless, based on the principle that one should introduce the Amidah prayer with praise of Hashem, it is worthy practice.
Aleinu is part of the prayer service, and for an individual Amidah that one davens outside the institutional service, there does not appear to be a reason to recite it.
Best wishes.
