Question: What are the boundary lines of loyalties which when transgressed turn the doer into a Kaafir (disbeliever), outside the pale of Islaam? We hear that anyone who eats or sits with a Mushrik (one who associates others with Allaah in His Divinity or worship), or uses the light of their lamps, or sharpens for them a pencil, or fills their inkwell is a Mushrik like them. We often deal with Jews and Christians because of citizenship and coexistence in one place. What are then the limits of loyalties which when transgressed renders the doer of the act a disbeliever? What are the books that deal with this matter in detail? Are loyalties to Allaah and Muslims from the fundamental requirements of testifying that there is no god in truth but Allaah?
Answer: Loyalties to disbelievers that render a Muslim a disbeliever is loving and supporting them against Muslims, but they do not include dealing with them justly, associating with them to call them to Islaam, attending their meetings and traveling to their land for clarifying and spreading Islaam… read more here.