Sunan Ibn Majah, Hadith 3505 ⓘ
It was narrated from Abu Hurairah that the Prophet said: “If a fly falls into your drink, dip it into it then throw it away, for on one of its wings is a disease and on the other is a cure.”
حَدَّثَنَا سُوَيْدُ بْنُ سَعِيدٍ، حَدَّثَنَا مُسْلِمُ بْنُ خَالِدٍ، عَنْ عُتْبَةَ بْنِ مُسْلِمٍ، عَنْ عُبَيْدِ بْنِ حُنَيْنٍ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ " إِذَا وَقَعَ الذُّبَابُ فِي شَرَابِكُمْ فَلْيَغْمِسْهُ فِيهِ ثُمَّ لْيَطْرَحْهُ فَإِنَّ فِي أَحَدِ جَنَاحَيْهِ دَاءً وَفِي الآخَرِ شِفَاءً " .
also referenced under: Book 31, Hadith 3634 (In-Book) & Volume 4, Book 31, Hadith 3505 (DarusSalam)