During my Zuhr Qasr, when I joined late, in the 4th rakaat behind an Imam, after standing up after Salaam, do I pray remaining 3 rakaats or just 1 rakaat? How about when Imam is also doing Qasr? What if I don’t know if Imam is doing Qasr or not?
1. If you got up so much that you were closer to standing then sitting i.e. you had straightened your legs, then it would be necessary to make sajda as-Sahw. If you were closer to sitting, then returned, Sajda us-Sahw would not be neccessary. (Imdaad al-Fataah Pg.516)
2. If you are a musafir who is performing salah behind an Imam, then you would adopt the salah of the Imam ie. if he is a Musafir as well, you would perform Qasr and if not then you would perform complete salah. Thus in this case, you should have read 3 Rakaat after salaam not one.
If the Imam is a musafir, then he should make an announcement straight after the salam, informing the congregation that he is a musafir, thus if any of them is not one, he should complete his salah.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai