Combining prayers :There is no difference - between all the Islamic schools of thought amongst the ahl al-qibla - in allowing the combination of the two obligatory prayers, al-zuhr and al-`asr , at `Arafa at the time of the noon ( al-zuhr ) prayer. Technically, this is [called] jam' al-taqdim (the preceding combination). Similarly, there is no difference between them in allowing the combination of the two obligatory [prayers] - al-maghrib and al-`isha' - at al-Muzdalifa at the time of the `isha' [prayers]. Technically, this is called jam' al-ta'khir (the delayed combination). There is no difference [amongst the scholars] in preferring these two combinations. Indeed, they are amongst the prophetic practices. However, they (the scholars) have differed as to the permissibility of combining the prayers in other instances.
The point of disagreement here is the permissibility of combining two obligatory prayers by performing them together at the time stipulated for one of them either by bringing it forward ( taqdiman) as at `Arafa or by delaying it ( ta'khiran ) like the combination in al-Muzdalifa.
The Imams from the family of Muhammad (S.A.W.) have declared that this is permissible at all times although it is better to separate them. Their followers (Shi`as) have followed them in this [ruling] at all times and places. Most of the time, they combine al-zuhr and al-`asr and [also] al-maghrib and al-`isha' , whether they are travelling or at home, whether they have an excuse [to combine] or without an excuse. Jam' al-taqdim and jam' al-ta'khir are equally valid for them [at all times].