أَخْبَرَنَا قُتَيْبَةُ قَالَ حَدَّثَنَا سُفْيَانُ عَنْ الزُّهْرِيِّ عَنْ أَبِي سَلَمَةَ عَنْ أَبِي هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ مَنْ قَامَ شَهْرَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ

It was narrated from Abu Hurairah that : The Messenger of Allah [SAW] said: "Whoever stands (in he voluntary night prayer of) the Ramadan out of faith and in the hope of reward, his previous sins will be forgiven." Translation Not Available

Book Ref: Sunan An Nisai Book 47 Hadith 5024
Web Ref:  Sunan An Nisai Vol 6 Book 47 Hadith 5027