All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
Labeling a Muslim as a disbeliever is a very serious matter that must not be taken lightly. The basic principle is that the person whose Islam is established with certainty cannot be declared otherwise based on mere doubts. Therefore, such satanic whisperings and doubts must be simply overlooked and disregarded. If a person hates to commit disbelief, then that is proof that he is a believer. It has been narrated on the authority of Abu Hurayrah, may Allah be pleased with him, that a group of the Companions said to the Prophet, sallallahu ‘alayhi wa sallam, "Verily we find in our minds that which every one of us considers it too grave to express in words." He, sallallahu ‘alayhi wa sallam, said, "Do you really find it?" They said, "Yes." Upon this, he, sallallahu ‘alayhi wa sallam, remarked, "That is explicit faith." [Muslim]
Having doubts regarding one's belief is a kind of Waswasah (obsessive whisperings) from the work of Satan. When the Muslim experiences such whisperings, he is enjoined to disregard them and pay absolutely no attention to them. He should also seek refuge with Allah from the accursed Satan. Ibn ‘Abbaas, may Allah be pleased with him, narrated that a man came to the Prophet, sallallahu ‘alayhi wa sallam, and said, "O Messenger of Allah! One of us has thoughts of such nature that he would rather be reduced to charcoal than to speak about them." He, sallallahu ‘alayhi wa sallam, said, "Allah is Most Great; Allah is Most Great; Allah is Most Great! Praise be to Allah, Who reduced the guile of the devil to mere evil prompting (Waswasah)." [Ahmad and Abu Daawood]
We implore Allah to bless us with safety and wellbeing from all evils and tribulations.
Allah knows best.