Sunan an-Nasa'i 2203
سنن النسائي#2203SahihIt was narrated from Abu Hurairah that the Prophet said:"Whoever fasts in 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
In-book reference: 22:114