Source : Webster's Revised Unabridged Dictionary (1913)

Disbelieve \Dis`be*lieve"\, v. t. [imp. & p. p. {Disbelieved};
   p. pr. & vb. n. {Disbelieving}.]
   Not to believe; to refuse belief or credence to; to hold not
   to be true or actual.

         Assertions for which there is abundant positive
         evidence are often disbelieved, on account of what is
         called their improbability or impossibility. --J. S.
                                                  Mill.

Source : WordNet®

disbelieving
     adj : denying or questioning the tenets of especially a religion;
           "a skeptical approach to the nature of miracles" [syn:
           {skeptical}, {sceptical}, {unbelieving}]