Question: What is the separating line between Kufr (disbelief) and Islaam? What about a person who utters the Two Testimonies of Eemaan, and then commits actions that contradict them, is he a Muslim, despite his Salaah (prayer) and way of life?
Answer: The separating line between Kufr (disbelief) and Islaam is uttering the Two Testimonies of Eemaan with truthfulness and sincerity and acting accordingly. Whoever fulfills this, is a Muslim and a believer. As for those who show hypocrisy and do not believe, or are insincere, they are not believers… read more here.