If someone has waswas about leaving the fold of islam how can he combat it Repeating shahada
if you have a difficult time understanding matters regarding Islam's teachings or some topics that Islam treats, you should ask about them and get the doubt clear because I assure you every unclear matter has its proper answer, but Satan makes you doubt everything without letting you see any effective solution to your problem. I also advise you to take some private time to think and see God's greatness through his creatures and read Quran to see how it can not be written by anyone else but God. Read about our prophet's life (peace be upon him) and see how great our religion is. Doubting without finding a solution to your thoughts is of no use. May Allah guide you.