He was the son of one of "The Five Siyyids" (Sádát-i-Khams in Arabic), so named by Bahá'u'áh. For the story of this family see The Khamsis: A Cradle of True Gold by Boris Handal. Mas'ud Khamsi's story is told in this book (p111-239).
Khamsis, The: A Cradle of True Gold, by Boris Handal (2020). Biography of the five-brother Báqirof-Khamsi clan, designated by Bahá'u'lláh as the "Five Siyyids" after they accepted the Bahá'í Faith in 1881. [about]