In Parks v. Zitnik, 453 So. 2d 434 (Fla. 2d DCA 1984), the district court stated that the trial court erred in allowing questioning with regard to the specifics of the appellant's criminal history. The appellee contends that any error committed by the trial court was harmless because the case was tried by the court rather than by a jury. Since the parties did not request a jury trial, the trial judge had to determine the credibility of the parties. Jalbert v. State, 95 So. 2d 589 (Fla. 1957). Due to the nature of this case, the credibility of the parties was crucial and therefore we cannot hold the error was harmless. Had the trial judge stated that he based his findings only upon certain evidence and that he disregarded the challenged evidence, the error, if any, in the admission of such evidence could have been determined harmless. Capitoli v. State, 175 So. 2d 210 (Fla. 2d DCA 1965). Where the proof of guilt is so convincing that a person would clearly have been found guilty even without collateral evidence introduced in violation of the evidence code, the violation of the code may be considered harmless. In the case sub judice, however, because of the importance of the credibility of the witnesses under the particular facts of this case, we cannot say the evidence in favor of the appellee was so clear and convincing that introduction of the challenged evidence was harmless. A trial judge is presumed to rest his judgment on admissible evidence and to disregard inadmissible evidence, United States v. Masri, 547 F.2d 932 (5th Cir. 1977), but in view of the specific findings of admissibility in this case, we cannot hold the trial court disregarded inadmissible evidence. Parks, 453 So. 2d at 437.