Sahih al-Bukhari
Book 2: Belief
كتاب الإيمان
51 hadith in this book
Chapter 28 To observe fasting (according to Islamic teachings)] during the month of Ramadan (sincerely and faithfully) hoping for Allah's Reward only, is a part of faith
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."
حَدَّثَنَا ابْنُ سَلاَمٍ، قَالَ أَخْبَرَنَا مُحَمَّدُ بْنُ فُضَيْلٍ، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ صَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ ".
Hadith text, translations and grading are courtesy of Sunnah.com.