When does a person become a disbeliever (kafir)?

A Muslim is not deemed an apostate unless they commit a saying, action, or belief that the Qur'an and Sunnah indicate, or upon which scholars have unanimously agreed, to be major disbelief (kufr akbar) that expels one from the faith. Examples include insulting Allah and His Messenger, denying what is known by necessity to be part of the religion, prostrating to an idol, supplicating to the dead, aiding disbelievers against Muslims, believing in the world's pre-eternity or Allah's incarnation in His creation, or doubting the resurrection. For a Muslim to be declared an apostate, they must be an adult, of sound mind, acting voluntarily, and not excused by ignorance or misinterpretation, where ignorance and misinterpretation are considered valid excuses.