Sunan an-Nasa'i
The Book of al-Fara' and al-'Atirah
كتاب الفرع والعتيرة
Chapter 11
الذُّبَابِ يَقَعُ فِي الإِنَاءِ
Translation
Abu Saeed al-Khudri reported that the Prophet said: If a fly falls into one of your vessels, immerse it.