The virtue of fasting ‘Ashoora’

I heard that fasting the day of ‘Ashoora’ expiates for the past year, is this true?
Does it expiate for everything, even major sins? What is the reason for venerating this day?.

Praise be to Allaah.

Firstly:

Fasting the day of ‘Ashoora’ does expiate for the past year, because the Prophet (peace and blessings of Allaah be upon him) said:

“Fasting the day of ‘Arafah I hope Allaah will expiate thereby for the year before it and the year after it, and fasting the day of ‘Ashoora’ I hope Allaah will expiate thereby for the year that came before it.”

Narrated by Muslim, 1162.