This is a tough one. (Except for the misspelling. I fixed that.)
Harlan Ellison's own page (approved but not maintained by him, he hates computers) cites this quotation but doesn't give a definitive source.
I've seen similar quotations from Zappa (including the one you posted) but whether this originated with him is another story.
I would welcome a definitive reference one way or the other, but I'm leaning toward Ellison.
BTW, no, Ellison isn't noted for his humility, but read any interview with him and you'll quickly understand that he is a devout believer in everyone else's