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