Wulan, S, and D Pratiwy. “The Spiritual States (Ahwal) in the Rubaiyat of Omar Khayyam”. KnE Social Sciences 3, no. 4 (April 19, 2018): 864–877. Accessed September 20, 2019. http://kne-publishing.com/index.php/Kne-Social/article/view/1993.