What is the relationship between 'aqidah (creed/dogma) and iman (faith/belief), and does an increase in 'aqidah lead to an increase in iman? How is their saying "The 'aqidah is fixed, and iman increases and decreases" interpreted alongside their saying that "Iman increases and decreases" falls within the concept of 'aqidah? What is the linguistic and technical definition of 'aqidah, and when did this concept emerge?

The phrase "Creed is constant, while faith increases and decreases" was not authenticated from the early Salaf imams. However, it was authenticated from Ibn Taymiyyah that faith is composed of a foundation without which it is incomplete, an obligation that diminishes if missed, and a supererogatory act whose omission leads to the loss of a higher degree. Thus, people in this regard are: those who wrong themselves, those who are moderate, and those who are foremost. Believers vary in their faith according to the strength of their certainty, their affirmation, their love for Allah, their hope, their fear, their reliance upon Him, their submission to His judgment, and their contentment with His decree, as well as according to their performance of good deeds and their avoidance of prohibitions.