In Origin of the Species Darwin rejected the idea of 'special creation' outright. In chpt 14 on Page 487 he wrote:
"As species are produced and exterminated by slowly acting and still existing causes, and not by miraculous acts of creation and by catastrophes;
He was talking about the origin of the varied species - not of life itself.
He was rejecting the notion that all species were created in their present form, not that there was no special creation.
He also held the view that all the life that existed descended from 'one primordial form' as opposed to many created forms for he wrote in his conclusion on Page 484
" Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed."
"Into which life was first breathed."? Sounds like he was expressing that there was one original life, specially created (allusion to Genesis creation story) from which all species originate.
The above article from Pubmed Central shows that there were numerous other evolutionists who were discussing 'spontaneous generation' as a part of evolution. German geologist Heinrich George Bronn who translated The Origin of Species in 1860 even added a chapter about how spontaneous generation fitted in with Darwin’s theory.
So it is quite true that those early evolutionists were in fact making such claims and this is why creationists were so opposed to their ideas.
So Darwin didn't call it 'descent with modification' he called it 'spontaneous generation'. As if it were different. Of course, it is true that if an account for the origin of life could be settled - it would complete the naturalistic account for the existence of life which I'm sure Darwin would be happy to find (as the quote suggests).
Nobody suggests they are unrelated in so far as natural history is concerned. It's just that disproving one, does not disprove the other.