On the authority of Abu Hafsah (may Allah be pleased with him) it is related that the Prophet (peace be upon him) said,
“Fasting on the day of ‘Arafah absolves the sins for two years: the previous year and the coming year, and fasting on ‘Ashura, (the tenth day of Muharram) atones for the sins of previous years.”
And then,
The Prophet [saw] said, “Fasting the day of Ashura....I hope that Allah will accept it as an expiation for [the sins committed in] the previous year.” [Muslim]
Why do we have two fast days that do the same thing so close together?
“Fasting on the day of ‘Arafah absolves the sins for two years: the previous year and the coming year, and fasting on ‘Ashura, (the tenth day of Muharram) atones for the sins of previous years.”
And then,
The Prophet [saw] said, “Fasting the day of Ashura....I hope that Allah will accept it as an expiation for [the sins committed in] the previous year.” [Muslim]
Why do we have two fast days that do the same thing so close together?