What is the ruling regarding fasting the Day of Arafah and the Day of Ashura?

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Fasting the Day of Arafah is recommended; the Prophet, peace be upon him, stated regarding its fast: "I seek from Allah that it expiates the year preceding it and the year following it." Regarding the fast of Ashura, he stated: "I seek from Allah that it expiates the year preceding it." This was narrated by Muslim.