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".  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ صَامَ يَوْمًا فِي سَبِيلِ اللَّهِ زَحْزَحَهُ اللَّهُ عَنِ النَّارِ سَبْعِينَ خَرِيفًا أَحَدُهُمَا يَقُولُ سَبْعِينَ وَالآخَرُ يَقُولُ أَرْبَعِينَ  

That the Prophet ﷺ said: "A worshipper does not fast a day in the cause of Allah except that, that day (of fasting) distances the Fire from his face by seventy autumns."  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَصُومُ عَبْدٌ يَوْمًا فِي سَبِيلِ اللَّهِ إِلاَّ بَاعَدَ ذَلِكَ الْيَوْمُ النَّارَ عَنْ وَجْهِهِ سَبْعِينَ خَرِيفًا  

That the Prophet ﷺ said, "Whoever fasts a day in the cause of Allah, Allah shall put between him and the Fire a trench whose distance is like that between the heavens and the earth." This Hadith is Gharib as a narration of Abu Umamah.  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ صَامَ يَوْمًا فِي سَبِيلِ اللَّهِ جَعَلَ اللَّهُ بَيْنَهُ وَبَيْنَ النَّارِ خَنْدَقًا كَمَا بَيْنَ السَّمَاءِ وَالأَرْضِ هَذَا حَدِيثٌ غَرِيبٌ مِنْ حَدِيثِ أَبِي أُمَامَةَ