What is the ruling on one who says to a group of Muslims: "You are apostates," because of their cooperation with a disbeliever to harm Muslims, and does the verse apply to them: "And whoever among you takes them as allies is indeed one of them"?

Assisting disbelievers against Muslims takes two forms: The first is motivated by love for them and a desire for their victory, and this is an act of disbelief that expels one from the fold of Islam, by the consensus of scholars. The second is motivated by personal interest or fear, and this is forbidden and considered a grave major sin, but it does not reach the level of disbelief that expels one from the fold of Islam. An example of this is the story of Hatib ibn Abi Balta'ah, may Allah be pleased with him.