Is the heart's lack of conviction regarding the innovativeness of communal Dhikr (remembrance of Allah) and fasting—knowing that these are innovations that did not exist during the time of the Messenger of Allah, may Allah bless him and grant him peace, and adhering to refraining from them—considered disbelief or a denial of the Messenger of Allah, may Allah bless him and grant him peace?

The questioner is suffering from whispers (waswas) related to disbelief (kufr), including her whispers about congregational dhikr (remembrance of Allah). Performing congregational dhikr in one voice is an innovation (bid'ah), as there is no proof of it from the Prophet (peace be upon him) or his companions. However, one who is not convinced that it is an innovation is not deemed a disbeliever. It is advised to turn away from these whispers and not to dwell on them, as the best cure for them is complete avoidance.