Explanation of Apostasy and When It Occurs

Question:
The questioner says: What is apostasy? When does apostasy occur in belief? And is the apostasy of a person of discernment valid?

Answer:
Apostasy is turning away from Islam. Apostasy is turning away from Islam from following to returning. Turning away from Islam occurs by committing one of the nullifiers of Islam, which is a major sin against Allah the Exalted.
It occurs through speech, it occurs through action, it occurs through belief, and it occurs through prostration. These are the four matters. If one speaks words of disbelief and it is not absolute, meaning it merely crosses his mind, and if he performs an act of disbelief, such as prostrating to other than Allah or slaughtering for other than Allah, or if he abandons the prayer, this error expels him from Paradise.
And if he believes in his heart that what the Messenger (peace and blessings be upon him) brought is not true, or if he believes that the Prophet (peace and blessings be upon him) is not a messenger, like the state of the hypocrites. The hypocrites testify that he is the Messenger of Allah, but they lie in their inner selves. This is apostasy of certainty or doubt. He says: I do not know if it is true or not true, if he is a messenger or not a messenger? Is what he said true? Is what he mentioned about Paradise and Hellfire true or impossible?
A branch of apostasy. So apostasy occurs through speech, through action, through belief, and through doubt. The nullifiers are many. The Shaykh Muhammad ibn 'Abd al-Wahhab (may Allah have mercy on him) mentioned ten nullifiers in a separate treatise, and the jurists mentioned many nullifiers in the books of jurisprudence.