The Book Of Faith and its Signs
47/21. Chapter:
Praying Qiyam in Ramadan
Sunan an-Nasai
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."
Reference : Sunan an-Nasa'i 5024In-book reference : Book 47, Hadith 40English translation : Vol. 6, Book 47, Hadith 5027