Musannaf Ibn Abi Shayba 27:370

Abu Mu'awiyah narrated to us, from 'Asim, from Abu 'Uthman, that there was a staff in his hand which he would lean upon while walking. He used to frequently say, "By Allah, if I wished for this staff of mine to speak, it would speak. If 'Umar ibn al-Khattab were a scale, there would not be the weight of a hair in it [that was crooked or unjust]."