Question:
What is the ruling on a Muslim that calls another Muslim kafir and publishes it?
Answer:
Ibn `Abidin in his Rasa’il (2:291 Sall al-Husam al-Hindi) said that a Muslim who unjustly calls another Muslim kafir commits kufr if he really considers him kafir but not if he only intends to insult him. In the latter case he only commits fisq. We seek refuge in Allah from the accusations of the ignorant and the fitan of our times.
Hajj Gibril