Loyalty to Kafirs that takes one out of Islam
What are the boundary lines of loyalties which when transgressed turn the doer into a Kafir (disbeliever), outside the pale of Islam? We hear that anyone who eats or sits with a Mushrik (one who associates others with Allah 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 Allah and Muslims from the fundamental requirements of testifying that there is no god but Allah?
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 Islam, attending their meetings and traveling to their land for clarifying and spreading Islam.
May Allah grant us success. May peace and blessings be upon our Prophet, his family and Companions