Mohd Tajuddin, A.R. , Rosdi Zakaria. “Discussion of Instructional Methods and Subjects by Caliph Harun ArRasyid (786-810AD) Educational Speech”. International Journal of Advanced Science and Technology, Vol. 29, no. 7s, Apr. 2020, pp. 398 -02, https://sersc.org/journals/index.php/IJAST/article/view/9454.