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According to Ahl-ul-Sunnah wal-Jama`ah (adherents to the Sunnah and the Muslim mainstream), faith is shown through words and deeds and it increases and decreases. It increases if a person obeys and remembers Allah and decreases if they are heedless and commit sins.
Selected from: Fatwas of Ibn Baz, Volume 5, Part No. 5; Page No. 11, Article: The essence of `Ibadah and Tawhid of the Creator
https://www.alifta.gov.sa/En/IftaContents/IbnBaz/Pages/default.aspxcultStr=en&View=Page&PageID=438&PageNo=1&BookID=14
