We affirm appellant’s conviction and sentence. Although we agree with appellant that the trial court erred in allowing a prosecution witness to be impeached, we find such error to be harmless beyond a reasonable doubt. State v. DiGuilio, 491 *897So.2d 1129 (Fla. 1986). Our conclusion is mainly predicated upon the admission of other substantial evidence concerning the witness’ prior identification of the appellant as his assailant.