Is it permissible for a traveler to combine Asr with Dhuhr, as a delayed combination (jam' ta'kheer), if he strongly believes he will arrive before Maghrib?

It is permissible for a traveler to combine two prayers, either by performing them earlier (taqdim) or delaying them (ta'khir), and he should do what is easier for him. If the sun declines while he is still traveling, then it is better for him to combine by delaying. If he does so and reaches his destination before sunset, the combination is valid, and he does not need to repeat the prayers.