Mazidah bin Jabir narrates from his mother that during the caliphate of Hazrat Uthman (may Allah be pleased with him), I was once in the mosque of Kufa. At that time, our leader was Hazrat Abu Musa Ash'ari (may Allah be pleased with him). I heard him saying that the Messenger of Allah (peace and blessings be upon him) has commanded to fast on the tenth of Muharram, so you should also fast.