Is it permissible for a taxi driver to combine the Dhuhr and Asr prayers, and the Maghrib and Isha prayers, by performing them earlier (jam' taqdim) or later (jam' ta'khir) when necessary, given that he sometimes prays after the time for the prayer has expired?

Every Muslim must perform the prayer at its prescribed time, and deliberately delaying it is one of the major sins. It is not permissible to combine two prayers except for an excuse. It appears that the aforementioned driver has no excuse preventing him from performing the prayer before its time expires. However, if he needed to combine them and would be harmed by not doing so, some scholars have permitted combining prayers out of necessity. This is a concession, and it is hoped that there is no harm in it when there is a dire need, while knowing that the original principle is to perform each prayer at its designated time.