It wasnarrated from Abu Sa'eed Al-Khudri that the Messenger of Allah(ﷺ) said:
"Whoever fasts one day in the cause of Allah, Allahwillkeep the Fire away from his face the distance of seventy autumns(years) for that day." (ID)
English reference (ID): Vol. 1, Book 7, Hadith 1717 (ID)
Arabic reference (ID): Book 7, Hadith 1788 (ID)