Hazrat Usman was assassinated in Muharram
The first Capital for Abbasid Caliphate was Kufa from 750-762 AD
The first caliph of Fatimids was Abdullah al Mahdi
Diwan al Hisbah was constituted under Abbasids during the reign of Caliph Al-Mansur(http://en.islamstory.com/hisbah-isla...istration.html)