Combining and shortening the prayers while travelling

Answer

According to the schools that allow combining prayers, one may do so either in the time of the first prayer (asr in the time of zuhr; isha in the time of maghrib) or in the time of the second. If combining in the time of the second prayer, one must (1) intend during the first prayer's time to delay it until the second, and (2) remain a traveller until the second prayer ends. If combining both in the time of the first prayer, one must (1) pray the first prayer (zuhr or maghrib) first, (2) intend to combine sometime during it, (3) not separate the two by a gap long enough to pray two rak'ahs (performing only the integrals, hastening into the second right after), and (4) remain a traveller until completing the opening takbir of the second prayer. Additionally, a traveller may shorten the four-rak'ah prayers to two, provided (1) the travel is permissible and valid, meeting all necessary conditions, (2) one has prior knowledge of the permissibility and method, (3) one intends to shorten the prayer at the opening takbir, and (4) one remains a traveller until the prayer's end.