Question: What is the ruling on a person who claims to be Muslim by mouth only, saying: “I am a Muslim,” while practicing Bid`ahs (innovations in religion) and acts of Shirk (associating others with Allaah in His Divinity or worship). Is this person truly a Muslim? Is it permissible to eat from their slaughtered animals?
Answer: Whoever utters the two testimonies of faith believing in their significance and acting accordingly, is a believing Muslim. But whoever commits acts contradictory to their significance is a Kaafir (disbeliever) even if they utter them, perform Salaah, and observe Sawm (Fast)… read more here.