What is the difference between a person afflicted with obsessive-compulsive disorder (OCD) concerning creed and the doubt that expels one from the fold of Islam, and why is the person afflicted with OCD excused while both harbor the same doubts?

There is a great difference between waswasah (whispers/obsessive thoughts) and doubt that expels one from the religion. Waswasah consists of fleeting thoughts that do not settle in the heart and are disliked by the one experiencing them, and a Muslim is not held accountable for them. As for doubt that expels one from the religion, it is a suspicion that settles in the heart, negating the firm conviction in Allah's news. Examples of doubt that expels one from the religion include the disbelief of doubt and conjecture, which is hesitation in believing in the universally agreed-upon fundamentals of religion, or the lack of firm conviction in accepting news or a ruling that is necessarily established in religion, such as doubting the authenticity of the Qur'an or the reality of the torment of the grave.