Sunan an-Nasa'i 2200
سنن النسائي#2200SahihIt 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
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 22:111