It was reported from Abu Qutaadah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) was asked about fasting on the Day of Arafah. He said, “It expiates for the sins of the previous year and of the coming year.” [Muslim]
It was narrated from Aa’ishah (may Allah be pleased with her) that the Prophet (peace and blessings of Allah be upon him) said: “There is no day on which Allah frees more people from the Fire than the Day of Arafah. He comes close and expresses His pride to the angels, saying, ‘What are these people seeking?’” [Muslim]