Fasting on the day of Arafah expiates the sins of the year and the year that follows, and fasting on the day of Ashura expiates the sins of one year. Sufyan did not narrate it to us as marfu, though it is in fact marfu.
حدثنا سفيان قال سمعناه من داود بن شابور عن أبي قزعة عن أبي الخليل عن أبي حرملة
صيام عرفة يكفر السنة والتي تليها وصيام عاشوراء يكفر سنة لم يرفعه لنا سفيان وهو مرفوع
Its isnad is sahih. It has appeared previously at 22416, except that here it is presented as stopped (mawquf), while in the following one it will be presented as raised (marfu). Dawud bin Shabur is trustworthy, and his hadith appears in the Sunan. Abu Qazaa is Suwayd bin Hujayr Bahili, and he is trustworthy, his hadith also appearing in the Sunan. Abu Khalil is Abdullah bin Khalil, and he is trustworthy, his hadith also appearing in the Sunan. Abu Harmalah is Harmalah bin Iyas, whom Ibn Hibban deemed trustworthy, while Abu Hatim said, "There is no harm in him," though there is much variation in his hadith. However, he has a corroborating narrator.