Quilliam = Henri M. de Leon (a great piece of evidence)

Ron Geaves' biography of Abdullah Quilliam, England's first prominent convert to Islam, provided a number of pieces of evidence that supported the by now well-accepted idea that Quilliam used the pseudonym Henri M. de Leon while living in London after 1912. However, despite the numerous pieces of strong circumstantial evidence presented by Geaves, I always felt that what was missing was a single piece of evidence that undeniably confirmed that the two men were one and the same.

I believe I have just found what I've been looking for.

Exhibit A: Quilliam's conversion story, as told by Quilliam to a reporter for a Muslim journal for an article that appeared in 1904.

Exhibit B: Henri M. de Leon's 1915 speech about his own conversion, which appeared in the January 1915 issue of the Islamic Review

(click to enlarge)

Now, Ron Geaves had already known about the 1915 speech, which he cited in his book (p. 271), and he knew that it had some general similarities with Quilliam's conversion story--but Geaves was not aware of the 1904 article, which contains the exact same, incredibly unique story as the 1915 speech: a Muslim in North Africa in the early 1880s pointing out to the future convert that the future convert's argument that Christianity is superior to Judaism because it's a later revelation can be used to say that Islam is superior to Christianity because it is an even later revelation.  

I'm finally satisfied.