Musnad Abu Ya'la al-Mawsili 155:26

Ibrahim ibn Muhammad ibn ‘Ar‘arah narrated to us, Ma‘n ibn ‘Isa narrated to us, Ibn Abi Dhi’b narrated to us, from ‘Uthman ibn Muhammad, from Sa‘id ibn al-Musayyib, from Abu Hurayrah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever is appointed as a judge, it is as if he has been slaughtered without a knife."