サヒーフ・アル＝ブハーリー #38
Sahih (Authentic)
Allah's Messenger (ﷺ) said, "Whoever observes fasts during the month of Ramadan out of sincere faith, and hoping to attain Allah's rewards, then all his past sins will be forgiven
伝承の連鎖（イスナード）
Narrated Abu Huraira