Ziyad bin Ayoub - Dulwiyya زياد بن أيوب بن زياد دلويه · Fasting (Kitab Al-Siyam)

'Ashurah was a day on which we used to fast in pre-Islamic days. When (fasting of) Ramadan was prescribed, the Messenger of Allah (ﷺ) said: This is one of the days of Allah ; he who wishes may fast on it.