Q. Do I have to perform short Salaah as a Musaafir if I am performing Salaah behind an Imaam who is performing full Salaah?
A. In the inquired case, if a traveller (Musaafir) is performing Salaah behind an Imaam who is a non-traveller (Muqeem), a traveller will perform the full Salaah behind the Imaam like a non-traveller.
A traveller will perform a short Salaah (Qasr) if he is leading a congregation in Salaah or if he/she is performing Salaah individually. (Mabsoot 2/105)
Allah Ta’ala Knows Best
Mufti Ismaeel Bassa
themufti.com