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."