Hasan, Awadh Ahmed. “Trends of Criticism Between the Two Caliphs: Omar Bin Alkhatab and Abdulmalek Bin Marwan: A Comparative Study of Environment Effect”. Arab Journal for Sciences and Research Publishing, vol. 7, no. 1, Mar. 2021, pp. 1-17, https://doi.org/10.26389/AJSRP.A101020.