(6) باب مَنْ صَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا وَنِيَّةً
Narrated Abu Huraira:
The Prophet (ﷺ) said, "Whoever established prayers on the night of Qadr out of sincere faith and hoping for a reward from Allah, then all his previous sins will be forgiven; and whoever fasts in the month of Ramadan out of sincere faith, and hoping for a reward from Allah, then all his previous sins will be forgiven."
Reference: Sahih al-Bukhari 1901
In-book reference: Book 30, Hadith 11
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 31, Hadith 125