Praise be to Allah.
If you have knowledge and understanding of the religion of Allaah that enables you to call others to Allaah and teach the people good things, and refute specious arguments and practise your religion openly among the kaafirs around you, then it is OK, because if a person who is as we have described and who has equipped himself with knowledge stays there, he can benefit himself and others. Allaah may guide many people through him if he strives hard in da’wah and is patient, and his intention is sincerely for Allaah alone. But if a person does not have this religious understanding or he does not have the patience for da’wah, or he fears that he may fall into things which Allaah has forbidden, or he cannot practise his religion openly by calling others to worship Allaah alone and warning them against shirk and explaining that to the people around him, then it is not permissible for him to stay among the mushrikeen, because the Prophet (peace and blessings of Allaah be upon him) said: “I have nothing to do with any Muslim who settles among the mushrikeen.” And because of the danger to which he is exposed by settling among them. And Allaah is the Source of strength.