Disbelief is to reject a tenet of the faith that we were commanded to believe in or to reject a matter clearly known to be of the religion.
See this link for more specifics.
Signs of Allah’s Nearness
https://seekersguidance.org/answers/general-counsel/obsessive-thoughts-about-disbelief/I struggle with thoughts of disbelief and suicide
Checked and Approved by Shaykh Faraz Rabbani
Shaykh Yusuf Weltch is a graduate from Tarim; a student of Habib Umar and other luminaries; and authorized teachers of the Qur’an and the Islamic sciences
Answers Team: For clarity on one’s faith and beliefs, take the Islamic Beliefs courses in the Seekers Islamic Studies Curriculum —
For beginners, we recommend: [Level One]
We also recommend Spirituality courses, including:
– OD Course on Why We Believe
– OD Course on 99 Names of Allah