Abu Sa'id Al-Khudri (RAA) narrated that The Messenger of Allah (ﷺ) said:
"No servant (of Allah) fasts on a day (merely) for the sake of Allah except that Allah pushes the Hellfire seventy years further away from his face, due to fasting on this day." Agreed upon and the wording is from Muslim.
English reference: Book 5, Hadith 702
Arabic reference: Book 5, Hadith 682