´It was narrated that An-Numan bin Abi 'Ayyash said:` "I heard Abu Saeed Al-Khudri say: 'The Messenger of Allah said: Whoever fasts one day in the cause of Allah will separate his face from the fire by (a distance of) seventy autumns."'
Hadith ReferenceSunan an-Nasa'i / The Book of Fasting / Hadith: 2251