It’s interesting the way creationists, if they can’t argue against what someone actually said, will argue against what they “must have meant.” It’s one of the traits that distinguishes creationism from real science.
But I think I’ve found what you’re referring to. Darwin did once speculate in a letter to a friend about life forming “in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present”—but he was doing so in the context of saying why such life wouldn’t survive today. He was not saying that that’s how he thought life began originally.
And besides, it was just speculation in a personal letter. What he was willing to say in print was “[how life itself first originated] are problems for the distant future, if they are ever to be solved by man” (Descent of Man, chapter 3) and “our ignorance is as profound on the origin of life as on the origin of force or matter” (essay to the Atheneum, 1863). In other words, he didn’t know, and he didn’t think it was necessary to his theory.
Note the part about the origin of force or matter. Do you require physicists and chemists to state where those come from before you accept their theories about how they work?
And evolution is a fact. Living things once existed that don’t exist any more, and exist now that didn’t use to exist. The theory of evolution explains why that’s so.
It is also interesting how evolutionist ignore the hard argument to postulate about their own beliefs. The fact that there are things that did exist and don,t exist now are supposedly explained by extinction I have never heard anyone insinuate they evolved out of existence. As for things that now exist that did not exist I would say they got here the same as every other thing did, but that is the root of our discussion isn’t it. Of course we don’t want to talk about how that first thing evolved do we.