Sunan At-Tirmidhi

Narrated Abu Al-Aswad : From 'Urwah [bin Az-Zubair], and Sulaiman bin Yasar, that they reported to him from Abu Hurairah that the Prophet (ﷺ) said: ""Whoever fasts a day in the cause of Allah, Allah shall distance him from the Fire by seventy autumns."" One of them said ""seventy"" and the other said: ""forty"". [Abu 'Eisa said:] This Hadith is a Gharib Hadith from this route. Abu Al-Aswad's name is Muhammad bin 'Abdur-Rahman bin Nawfal Al-Asadi Al-Madani. There are narrations on this topic from Abu Sa'eed, Anas, 'Uqbah bin 'Amir, and Abu Umamah