Sunan an-Nasa'i, Volume 3, Book 22, Hadith 2233 (DarusSalam) ⓘ

It was narrated that Mutarrif said: "I entered upon 'Uthman bin Abi Al-As and he called for milk. I said: I am fasting; He said: "I heard the Messenger of Allah say: 'Fasting is a shield like the of any one of you in battle."' Abu Hurairah said: "The Messenger of Allah said: 'Fasting is a shield."' (Sahih

أَخْبَرَنَا عَلِيُّ بْنُ الْحُسَيْنِ، قَالَ حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنِ ابْنِ إِسْحَاقَ، عَنْ سَعِيدِ بْنِ أَبِي هِنْدٍ، عَنْ مُطَرِّفٍ، قَالَ دَخَلْتُ عَلَى عُثْمَانَ بْنِ أَبِي الْعَاصِ فَدَعَا بِلَبَنٍ فَقُلْتُ إِنِّي صَائِمٌ ‏.‏ فَقَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏ "‏ الصَّوْمُ جُنَّةٌ مِنَ النَّارِ كَجُنَّةِ أَحَدِكُمْ مِنَ الْقِتَالِ ‏" ‏ ‏.‏