Riyad as-Salihin 1219
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] .
وعن أبي هريرة رضي الله عنه عن النبي صلى الله عليه وسلم قال‏:‏ من صام رمضان إيمانًا واحتسابًا، غفر له ما تقدم من ذنبه ‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏