Abu Hurairah (May Allah be pleased with him) reported:
The Prophet (ﷺ) said, "He who observes fasting during the month of Ramadan with Faith while seeking its reward from Allah, will have his past sins forgiven."[Al-Bukhari and Muslim]. (ES)
App reference (ES): Book 9, Hadith 229 (ES)
Arabic/English book reference (ES): Book 9, Hadith 1219 (ES)