Sunan Abi Dawud, Hadith 3835

Abu Hurairah reported the Messenger of Allah as saying: when a fly alights in anyone’s vessel, he should plunge it all in, for in one of its wings there is a disease, and in the other is a cure. It prevents the wing of it is which there is a cure, so plunge it all in (the vessel).

حَدَّثَنَا أَحْمَدُ بْنُ حَنْبَلٍ، حَدَّثَنَا بِشْرٌ، - يَعْنِي ابْنَ الْمُفَضَّلِ - عَنِ ابْنِ عَجْلاَنَ، عَنْ سَعِيدٍ الْمَقْبُرِيِّ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِذَا وَقَعَ الذُّبَابُ فِي إِنَاءِ أَحَدِكُمْ فَامْقُلُوهُ فَإِنَّ فِي أَحَدِ جَنَاحَيْهِ دَاءً وَفِي الآخَرِ شِفَاءً وَإِنَّهُ يَتَّقِي بِجَنَاحِهِ الَّذِي فِيهِ الدَّاءُ فَلْيَغْمِسْهُ كُلَّهُ ‏" ‏ ‏.‏

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also referenced under: Hadith 3844 (DarusSalam)