Imaam Dhahabi (rahimahullaah) mentioned in the biography of Abbaadata that he was one who (liked) to joke and jest.  It was related that Abbaadata entered upon Al-Mutawakkil and he promised to beat him.  He (Mutawaakil) said (to Abbaadata): ”Did you slap the Imaam of the masjid?”  He (Abbaadata) said: O leader of the believers! I entered into the Masjid whilst I was in a hurry, so he led us for the Morning Prayer and prolonged it.  He recited a Juz until the sun was about to rise and I fell down.  Then after the Tasleem he said: ”Repeat your prayer because I was not in a state of ablution”, so I slapped him once.  Mutawakkil laughed.

[Taareekhul Islaam: 18/305]