Question 529: Is Eemaan (Faith) a whole which can never be divided? When a part of it is lost, is the rest lost too? If this is true, how can we reconcile between this claim and the fact that Eemaan is subject to increase and decrease?
Answer: Eemaan is divisible, as it increases and decreases. Allaah (Exalted be He) says: …And when His Verses (this Qur’aan) are recited unto them, they (i.e. the Verses) increase their Faith; and they put their trust in their Lord (Alone). Allaah (Exalted be He) also says: And Allaah increases in guidance those who walk aright. Loosing some of your Eemaan does not mean losing all of it; because the opinion that inclines to the loss of all of one’s Eemaan due to the loss of part of it is the doctrine of Al-Khawaarij (separatist group that believes committing a major sin amounts to disbelief)... read more here.