Sunan an-Nasa'i 2252
سنن النسائي#2252SahihIt was narrated from Abu Saeed Al-Khudri that the Prophet said:"Whoever fasts a day in the cause of Allah, Allah will separate his face from the heat of Hell (a distance of) seventy autumns
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: 22:163