The Increase (and Decrease) of Imaan (Faith)

Aali Imran (3):173
Those (i.e. believers) unto whom the people (hypocrites) said, “Verily, the people (pagans) have gathered against you (a great army), therefore, fear them.” But it (only) increased them in Faith, and they said: “Allâh (Alone) is Sufficient for us, and He is the Best Disposer of affairs (for us).”
Al-Anfal (8):2
The believers are only those who, when Allâh is mentioned, feel a fear in their hearts and when His Verses (this Qur’ân) are recited unto them, they (i.e. the Verses) increase their Faith; and they put their trust in their Lord (Alone);
At-Tawbah (9):124
And whenever there comes down a Sûrah (chapter from the Qur’ân), some of them (hypocrites) say: “Which of you has had his Faith increased by it?” As for those who believe, it has increased their Faith, and they rejoice.
Al-Ahzab (33):22
And when the believers saw Al­Ahzâb (the Confederates), they said: “This is what Allâh and His Messenger (Muhammad (sallallaahu alayhi wasallam)) had promised us, and Allâh and His Messenger (Muhammad (sallallaahu alayhi wasallam)) had spoken the truth, and it only added to their faith and to their submissiveness (to Allâh).
Al-Fath (48):4
He it is Who sent down As-Sakinah (calmness and tranquillity) into the hearts of the believers, that they may grow more in Faith along with their (present) Faith. And to Allâh belong the hosts of the heavens and the earth, and Allâh is Ever All-Knower, All-Wise.
Al-Muddaththir (74):31
And We have set none but angels as guardians of the Fire, and We have fixed their number (19) only as a trial for the disbelievers, in order that the people of the Scripture (Jews and Christians) may arrive at a certainty [that this Qur’ân is the truth as it agrees with their Books i.e. their number (19) is written in the Taurât (Torah) and the Injeel (Gospel)] and the believers may increase in Faith (as this Qur’ân is the truth) and that no doubts may be left for the people of the Scripture and the believers, and that those in whose hearts is a disease (of hypocrisy) and the disbelievers may say: “What Allâh intends by this (curious) example ?” Thus Allâh leads astray whom He wills and guides whom He wills. And none can know the hosts of your Lord but He. And this (Hell) is nothing else than a (warning) reminder to mankind.