Was this interest in Sufism more than merely a scholarly one for Quilliam? Was he a member of a Sufi Order?
Article: by Yahya Birt
“Today I received a rarity in the post that was published exactly a hundred years ago: a translated selection of the Ottoman Mevlevi Sufi poet Sheikh Haroun Abdullah’s (c.1556-c.1641) poems by Abdullah Quilliam. Quilliam had it privately published in 1916 under the pseudonym Henri M. Léon that he adopted on his return to England, c. 1909–10.  It was dedicated to his daughter, May Habeeba Quilliam, who had died at the age of eleven in May 1908 from diphtheria.  The volume was a matter of nostalgia for Quilliam as the translations had been undertaken on those occasions when he had been in Istanbul between 1903 and 1908…”
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Abdullah Quilliam and Sufism