The Book of Fasting (Kitab Al-Sawm)
Muslim :: Book 6 : Hadith 2570
Abu Sa'id al Khudri (Allah be pleased with him) reported Allah's Messenger (may peace be upon him) as saying: Every servant of Allah who observes fast for a day in the way of Allah, Allah would remove, because of this day, his face farther from the Fire (of Hell) to the extent of seventy years' distance.