Sunan Abi Dawud 2433
سنن أبي داود#2433Sahihحَدَّثَنَا النُّفَيْلِيُّ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ مُحَمَّدٍ، عَنْ صَفْوَانَ بْنِ سُلَيْمٍ، وَسَعْدِ بْنِ سَعِيدٍ، عَنْ عُمَرَ بْنِ ثَابِتٍ الأَنْصَارِيِّ، عَنْ أَبِي أَيُّوبَ، صَاحِبِ النَّبِيِّ صلى الله عليه وسلم عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " مَنْ صَامَ رَمَضَانَ ثُمَّ أَتْبَعَهُ بِسِتٍّ مِنْ شَوَّالٍ فَكَأَنَّمَا صَامَ الدَّهْرَ " .
Narrated Abu Ayyub:The Prophet (ﷺ) as saying: If anyone fasts during Ramadan, then follows it with six days in Shawwal, it will be like a perpetual fast
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:
In-book reference: 14:121