Sunan an-Nasa'i 2228
سنن النسائي#2228Sahihأَخْبَرَنَا إِبْرَاهِيمُ بْنُ الْحَسَنِ، عَنْ حَجَّاجٍ، قَالَ ابْنُ جُرَيْجٍ أَخْبَرَنِي عَطَاءٌ، عَنْ أَبِي صَالِحٍ الزَّيَّاتِ، أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الصِّيَامُ جُنَّةٌ " .
Abu Hurairah said:"The Messenger of Allah said: 'Fasting is a shield."' (Sahih)
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 22:139