Definition of Apostasy, Its Types, and the Nullifiers of Islam

Question:
May Allah reward you. Honorable Shaykh, the questioner asks: What is apostasy? When does apostasy occur in belief? And is the apostasy of a person of discernment established?

Answer:
Apostasy is turning away from Islam to whatever one turns back to. Returning to Islam occurs by committing one of the nullifiers of Islam. Disbelieving in Allah the Exalted and Majestic can be by speech, by action, by belief, or by prostration. These are the four matters. If one speaks words of disbelief and it is not ambiguous, then he falls into that. And if one performs an act of disbelief, such as prostrating to other than Allah, or slaughtering for other than Allah, or offering the prayer to other than Allah, this is what is reported from the people of Makkah.
And if one believes in his heart that what the Messenger (peace and blessings be upon him) brought is not true, or believes that the Prophet (peace and blessings be upon him) is not a messenger, like the state of the hypocrites, who testify that he is the Messenger of Allah but mock him in their private conversations, this is apostasy. Or doubt, saying: We do not know if it is true or not, if he is a messenger or not, if what he said is true, if what he mentioned about Paradise and Hell is true or not. If one doubts, this is disbelief, disbelief and apostasy. So apostasy is by speech, by action, by belief, and by doubt. The nullifiers are very numerous. 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.