Sunan an-Nasa'i 2253
سنن النسائي#2253SahihIt was narrated that Abu Saeed Al-Khudri said:"The Messenger of Allah said: Whoever fasts a day in the cause of Allah, Allah will separate his face (a distance of) seventy autumns from the fire in return for that day
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: 22:164