When is it permissible for a person to travel to the lands of disbelief?

Question:
I ask Allah for you, Your Eminence, father. The questioner says: If a person emigrates from a certain country, can he return to that country for a year or more?

Answer:
It is permissible for a person to go to the lands of disbelief while holding fast to his religion for worldly interests, such as going to learn expertise that is not found except with them, and which Muslims need, such as medicine, for example, where he travels to learn medicine, or to travel to learn industry and invention, and likewise trade, where he travels for the sake of trade to contract with factories and companies to buy goods; there is nothing wrong with that. He travels for the sake of treatment that is not found except with them.
These are matters for which there is nothing wrong with traveling, because they are interests, but on the condition that he holds fast to his religion, that he holds fast to his religion, and when his mission is over, that he returns to the lands of the Muslims, he returns to the lands of the Muslims when his mission is over. As for traveling for tourism and recreation in the lands of the disbelievers, this is not permissible; this is not permissible.