Musannaf Ibn Abi Shayba 4:848

Waki’ narrated to us, from Mahdi bin Maymun, from Ghaylan bin Jarir, from Abdullah bin Ma’bad al-Zamani, from Abu Qatada, that the Prophet, peace and blessings of Allah be upon him, was asked about fasting the day of Arafah. He said: "I anticipate from Allah that He will expiate [the sins of] two years: a year past and a year to come."