‘ASHURA عاشوراء
Lit. “the tenth” A voluntary fast day, observed on the tenth of the month of Muharram it is related that Muhammad observed it, and said it was a day respected by Jews and Christians (Mishkat. vii. vol. I.)
It is the only day of Muharram observed by the Sunni Muslims, being the day on which it is said God created Adam and Eve, heaven and hell, the tablet of decrees, the pen, life, and death. It is kept by the Sunnis as a fast. [MUHARRAM]

Based on Hughes, Dictionary of Islam