Sunan an-Nasa'i 2196
سنن النسائي#2196SahihAbu Salamah bin 'Abdur-Rahman narrated that Abu Hurairah said:"I heard the Messenger of Allah say concerning Ramadan: 'Whoeve spends its nights in prayer (Qiyam) out of faith and in the hope of reward, he will be forgiven his previous sins
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 22:107