Do all the actions of the heart increase and decrease? Please provide evidence.

The texts of the Quran and Sunnah indicate that faith (Iman) increases and decreases, and the Companions and their successors (Tabi'un) unanimously agreed on this. Some innovators (Ahl al-Bid'ah) hold that faith is merely affirmation (Tasdeeq), and that affirmation does not vary, and therefore, in their view, faith neither increases nor decreases. This is false. Scholars have explicitly stated that all acts of the heart increase and decrease without exception. The variation in faith occurs in multiple ways: outward actions, actions of the heart (such as love of Allah and humility of the heart), the affirmation and knowledge itself within the heart (in general and in detail), the essence of knowledge and affirmation, the causes of affirmation and love, and the continuity and steadfastness of these matters. Furthermore, acts of the heart affect affirmation; an increase in obligatory acts of the heart increases affirmation and certainty, while a decrease in them diminishes affirmation. Faith increases with acts of obedience, thereby increasing conviction (I'tiqad), verbal affirmation (Iqrar bi al-Lisan), and actions of the limbs (Amal bi al-Arkan). People vary in their affirmation, especially when it concerns a report about the unseen. The affirmation of one who affirmed the Messenger generally is not like that of one who knew what he reported in detail.