Is it permissible to combine the Dhuhr and Asr prayers, either by advancing or delaying them, for someone who travels every week from Muscat to his village, which is 300 km away, taking into consideration the Hanbali school of thought?

If the distance between your village and Muscat is 300 km, and your journey is permissible, then you are allowed to avail yourself of the concessions for travel, such as shortening and combining prayers. However, combining and shortening prayers is not permissible until after you have left the city's populated area. If the time for Dhuhr prayer begins before you depart from Muscat, it is not permissible for you to combine Asr prayer with it as a jama‘ taqdim (combining in advance) before leaving the populated area. In this case, you are required to perform the Dhuhr prayer in full, without shortening it.