How can a Muslim reinforce his faith?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

It is proven in the Quran and Sunnah, as well as by the sayings of the companions and many from the Taabi‘i generation, that faith increases and decreases, i.e. increases with obedience and decreases with disobedience.  This was stated by Imaam Al-Bukhari citing as evidence the Saying of Allaah The Almighty (which means): {That they would increase in faith along with their [present] faith.}[Quran 48:4] He also mentioned other verses and sayings of the Companions which prove that faith increases and decreases. Thus, whoever wants to increase his faith has to follow the commands of Sharee‘ah, abstain from doing what is prohibited and perform many good deeds.