Is it necessary to verbalize disbelief, or can a person become an apostate by his intention?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: Does a Muslim become an apostate by his intention in his heart, or is it necessary to verbalize apostasy with his tongue?

Answer:
You have heard that apostasy occurs by speech with the tongue and that apostasy occurs by belief, the belief of the heart, even if he does not verbalize it, even if he does not verbalize it, he becomes an apostate if he believes in disbelief and shirk (associating partners with Allah) in his heart, then he becomes an apostate.
And apostasy occurs by action, such as if he slaughters for other than Allah, or vows for other than Allah, or supplicates to other than Allah, or calls for aid from the dead, then he disbelieves with apostasy by speech.
And apostasy occurs by doubt, such as if he wavers regarding the validity of Islam or its invalidity, which is better for him, the state of the disbelievers or the state of the Muslims? If he wavers in his heart, he becomes an apostate, because this is doubt in the religion of Allah the Exalted. Yes.