المعنى الاصطلاحي :

The increase of a believer’s faith due to performing acts of obedience and good deeds, and its decrease due to disobedience of Allah and committing sins.

الشرح المختصر :

"Ziyādat al-imān wa nuqsānih" (increase and decrease of faith) is from the creed of Ahl-us-Sunnah wa al-Jamā‘ah. Faith increases and decreases, and the believers are of different levels of faith based upon their knowledge and actions. Therefore, some people have higher levels of faith than others. This is proven in several places in the Qur’an and Sunnah, and was stated by scholars from the righteous predecessors. Faith is of different levels and branches. It increases and decreases. It becomes stronger when one’s belief in Allah becomes stronger accompanied by an increase in good deeds – whether performed by the heart, the tongue, or the limbs. On the other hand, it decreases when a person commits sins and acts of disobedience. Therefore, if one obeys Allah, his faith will increase, but if he is unmindful of Allah or commits a sin, his faith will decrease. "Ziyādat al-imān wa nuqsānih" can occur in a variety of ways, which can be rounded up in two main categories: 1. Faith can increase due to Allah’s will. Indeed, Muslims were initially commanded with a certain amount of faith, then commanded with otherwise later on. 2. Faith may increase due the deeds of the person. In fact, faith of someone who fulfills all of the religious duties is not like that of someone who falls short of some of the duties. Every text that indicates that faith increases implies that it decreases as well, and vice-versa. This is because increase and decrease are inseparable concepts, and whatever increases must be liable to decrease.