(44) باب ثَوَابِ مَنْ صَامَ يَوْمًا فِي سَبِيلِ اللَّهِ عَزَّ وَجَلَّ وَذِكْرِ الاِخْتِلاَفِ عَلَى سُهَيْلِ بْنِ أَبِي صَالِحٍ فِي الْخَبَرِ فِي ذَلِكَ
It was narrated from Abu Saeed that he heard the Messenger of Allah say:
"There is no worshipper who fasts a day in the cause of Allah, the mighty and sublime, but Allah the mighty and sublime, will separate his face from the fire by (a distance of) seventy autumns in return for that day."
Reference: Sunan an-Nasa'i 2248
In-book reference: Book 22, Hadith 159
English translation: Vol. 3, Book 22, Hadith 2250