Sunan an-Nasa'i 2200
سنن النسائي#2200Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، قَالَ حَدَّثَنَا ابْنُ الْقَاسِمِ، عَنْ مَالِكٍ، قَالَ حَدَّثَنِي ابْنُ شِهَابٍ، عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " مَنْ قَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ " .
It was narrated from Abu Hurairah that the Messenger of Allah said:"Whoever spends the nights of Ramadan n prayer (Qiyam) out of faith and in the hope of reward, he will be forgiven his previous sins
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 22:111