Sunan an-Nasa'i 2204
سنن النسائي#2204SahihIt was narrated that Abu Hurairah said:"The Messenger of Allah said: 'Whoever fasts Ramadan 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: 22:115