(27) باب تَطَوُّعُ قِيَامِ رَمَضَانَ مِنَ الإِيمَانِ
Narrated Abu Huraira:
Allah's Messenger (ﷺ) said: "Whoever establishes prayers during the nights of Ramadan faithfully out of sincere faith and hoping to attain Allah's rewards (not for showing off), all his past sins will be forgiven."
Reference: Sahih al-Bukhari 37
In-book reference: Book 2, Hadith 30
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 2, Hadith 37