(1) باب فَضْلِ مَنْ قَامَ رَمَضَانَ
Narrated Abu Huraira:
I heard Allah's Messenger (ﷺ) saying regarding Ramadan, "Whoever prayed at night in it (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 2008
In-book reference: Book 31, Hadith 1
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 32, Hadith 226