Hadith 2203
Chapter 39: The Reward of one who prays Qiyam in Ramadan and fasts the month out of faith and hope for reward - كتاب الصيام
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " مَنْ صَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ " .
It was narrated from Abu Hurairah that the Prophet said:
"Whoever fasts in Ramadan out of faith and in the hope of reward, he will be forgiven his previous sins." '
Reference : Sunan an-Nasa'i 2203
In-book reference : Book 22, Hadith 114