What is the ruling on a doctor treating individuals from disbelieving, non-belligerent societies – who fight Muslims – with the aim of training (whether certification is available in his home country or not), or with the aim of permanent settlement in that country?

Residing in non-Muslim lands is not permissible for someone who cannot openly practice their religion, but it is not forbidden if one is able to openly observe religious rites and is safe from temptation. If residing there is permissible, then it is permissible to engage in transactions with them through buying and selling, except for anything that strengthens the non-believers against Muslims, such as weapons. The need of Muslims for the knowledge, industries, and technologies of non-believers may necessitate establishing relations with them. And whoever can dispense with residing among them, it is better for them to return to Muslim lands, due to the precautions associated with residing in non-Muslim lands.