(28) باب صَوْمُ رَمَضَانَ احْتِسَابًا مِنَ الإِيمَانِ
Narrated Abu Huraira:
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."
Reference: Sahih al-Bukhari 38
In-book reference: Book 2, Hadith 31
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 2, Hadith 38