Is it permissible for a Muslim to travel to the lands of the disbelievers to seek worldly knowledge, and is it permissible to assist disbelievers in producing military programs while they are at peace, and what is the ruling on money earned from this work?

Traveling to disbelieving countries for the purpose of acquiring beneficial worldly knowledge for Muslims is permissible if it cannot be obtained in Muslim countries, provided that the student is religious to safeguard against temptations. However, it is not permissible to assist the enemies of Allah in programs that may harm Muslims and increase the dominance of disbelievers over them, as Allah Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression). The doors of lawful sustenance are many, and whoever gives up something for the sake of Allah, Allah will compensate him with something better.