In the Quran, there's a clear separation between believers and disbelievers, but it doesn't talk of doubters as widely to best of my knowledge. Given that, I wonder whether there are references to doubters either in the Quran or hadiths, and whether Islam differentiates between doubters and disbelievers in any way. By doubter, I mean someone who doubts the correctness of Islam but does not necessarily thinks that it's false or/and working against it.