The ruling on one who prays in a direction other than the qiblah after exerting effort

Q: What is the ruling if it turns out that the prayer was performed in a direction other than the qiblah after exerting effort? Is there a difference between whether this occurred in a Muslim country, a non-Muslim country, or in the wilderness?

A: If a Muslim is traveling or in a land where it is not easy to find someone to guide him to the qiblah, his prayer is valid, provided he exerted effort in determining the qiblah and then it turned out that he prayed in a different direction.
However, if he is in the lands of the Muslims, his prayer is not valid; because he is able to ask someone to guide him to the qiblah, and he is also able to know the qiblah through the mosques.