Abu Sa'id Al-Khudri (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "Every slave of Allah who observes Saum (fasting) for one day for the sake of Allah, Allah will draw his face farther from Hell-fire to the extent of a distance to be covered in seventy years."[Al-Bukhari and Muslim].
App reference: Book 9, Hadith 228
Arabic/English book reference: Book 9, Hadith 1218