Here's something Darwin definitely did say about one (or two) of his premises (bold is from me):
I must here premise that, according to the view ordinarily received [PH here: I think he means creationism], the myriads of organisms, which have during past and present times peopled this world, have been created by so many distinct acts of creation. It is impossible to reason concerning the will of the Creator, and therefore, according to this view, we can see no cause why or why not the individual organism should have been created on any fixed scheme. That all the organisms of this world have been produced on a scheme is certain from their general affinities; and if this scheme can be shown to be the same with that which would result from allied organic beings descending from common stocks, it becomes highly improbable that they have been separately created by individual acts of the will of a Creator. For as well might it be said that, although the planets move in courses conformably to the law of gravity, yet we ought to attribute the course of each planet to the individual act of the will of the Creator. It is in every case more conformable with what we know of the government of this earth, that the Creator should have imposed only general laws. ...Source: The foundations of the Origin of Species: Two essays written in 1842 and 1844 by Charles Darwin.
This appears to be a variation of Occam's razor.
It is also the first of Newton's rules for conducting research.