Question 102: It is said that Riddah (apostasy) may be committed either by words or actions. I hope that you briefly clarify for me the verbal, practical and doctrinal forms of Riddah.
Answer: Riddah is reverting to Kufr (disbelief) after accepting Islaam. It may be by word, action, erroneous belief or doubt. Consequently, whoever associates other partners with Allaah; denies His Lordship, His Oneness, one of His Attributes or some of His Books or Messengers; curses Allaah or His Messenger; denies any of the consensually forbidden things or renders them lawful; denies one of the Five Pillars of Islaam or doubts their obligation; doubts Resurrection, the truthfulness of Muhammad (peace be upon him) or any of the Prophets or prostrates to an idol, a planet or the like, has disbelieved and apostatized from Islam. Please read the chapters discussing Riddah in the books of Fiqh (Islaamic jurisprudence), as scholars have elaborated on this topic.
Based on the above explanation, you can understand the verbal, practical, and doctrinal forms of Riddah... read more here.