A fashion is merely a form of ugliness so absolutely unbearable that we have to alter it every six months!
By Wilde in his spoken lecture on Personal Impressions of America at least as early as September 1883.
In a newspaper essay by Wilde:
The Philosophy of Dress, New-York Tribune, April 19th, 1885, 9. 
 This essay remained unknown to modern scholarship until its rediscovery in 2012 by John Cooper, the author of this web site.
Not in Mason.
Reused by Wilde in The Woman's World a magazine he edited:
Literary and Other Notes I, By The Editor. The Woman's World. November 1887. pp 36-40:
"And, after all, what is a fashion? From the artistic point of view, it is usually a form of ugliness so intolerable that we have to alter it every six months."
Magazine: Mason, 277.
In the First Edition of:
John Cooper, Oscar Wilde On Dress (CSM Press), 2013.