Houtsma and the story of the three school-fellows: Nizam al Mulk, Hasan B. Sabbah and ‘Umar Khayyam. S.Moinul Haq.
Journal of the Pakistan Historical Society, 28 (1953) 4, pp. 229–234.

The story of the three schoolfriends is generally considered to be controversial. The author however argues that there are authentic sources to support the story.