Perfect Rhymes (same vowel and ending sound):
* There are no perfect rhymes for "incredulous" in the English language.
Near Rhymes (similar vowel sound):
* Credulous
* Ludicrous
* Absurdulous (somewhat archaic)
Eye Rhymes (look similar but don't sound the same):
* Jealous
* Serious
* Previous
Slant Rhymes (some shared sounds but not exact):
* Suspicious
* Curious
* Dubious
Rhymes based on meaning:
* Unbelievable
* Astonishing
* Unfathomable
* Impossible
The best option depends on the context and the intended effect of your rhyme.