Principle: Belief is disbelief, but behavior is not disbelief

Question:
Honorable Shaykh, may Allah grant you success. The questioner says: One of the Shaykhs told me that there is a principle in declaring someone a disbeliever (takfir), which is that belief is disbelief, but behavior is not disbelief. Is this a correct principle?

Answer:
Disbelief (kufr) occurs through belief, through doubt, and through action. Disbelief has types, my brother; apostasy (riddah) has types. It occurs through belief, it occurs through doubt even if one does not hold the belief—if one doubts, it occurs. It also occurs through action. It occurs through speech: When they said what they said, apostasy occurs through speech. It occurs through belief, it occurs through doubt, and it also occurs through action, such as one who prostrates to an idol or slaughters for a grave. Is this an action or not? Yes, he becomes an apostate through the action.