Helmi Afizal bin Zainal. (2010). The concept of sin according to St. Augustine (430 A.D) and Al-Ghazali (1111 A.D): A comparative analysis. Kulliyyah of Islamic Revealed Knowledge and Human Sciences, International Islamic University Malaysia.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Helmi Afizal bin Zainal. The Concept of Sin According to St. Augustine (430 A.D) and Al-Ghazali (1111 A.D): A Comparative Analysis. Kuala Lumpur: Kulliyyah of Islamic Revealed Knowledge and Human Sciences, International Islamic University Malaysia, 2010.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Helmi Afizal bin Zainal. The Concept of Sin According to St. Augustine (430 A.D) and Al-Ghazali (1111 A.D): A Comparative Analysis. Kulliyyah of Islamic Revealed Knowledge and Human Sciences, International Islamic University Malaysia, 2010.