It is narrated from Hazrat Abu Qatadah (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: Fasting on the Day of Arafah (9th of Dhul-Hijjah) is an expiation for two years, and fasting on the Day of Ashura is an expiation for one year.
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 22588
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لاضطرابه والاختلاف فيه ، ولجهالة حرملة