Q. If someone reads full salaah instead of short salaah on travel, should they make qadha of those salaahs?
A. If a person performs a complete 4 Rakaats Fardh Salaah instead of a 2 Rakaats Fardh Salaah on a journey, mistakenly or due to miscalculation of the distance of travel etc., the Salaah performed will be valid. However, if the Salaah time remains and a person is made aware of his/her mistake, it will be necessary to repeat the Salaah during the Salaah time. If the Salaah time expires, it will not be necessary to repeat it.
On the other hand, if a person performs a complete 4 Rakaats Fardh Salaah instead of a 2 Rakaats Fardh Salaah on a journey knowingly and intentionally, it will be necessary to repeat all such Salaahs performed in this way. (Al Bahrur-Raaiq 2/141 – Khairul Fataawa 2/681-682)
Allah Ta’ala Knows Best
Mufti Ismaeel Bassa