Musnad Ahmad 30:1915

'Affan narrated to us, Hammad—meaning Ibn Salamah—narrated to us, he said: Thumamah ibn 'Abdullah ibn Anas informed us—and 'Affan said once: He said: That Thumamah claimed—from Abu Hurairah, from the Prophet, may Allah bless him and grant him peace; and from Habib ibn al-Shahid, from Muhammad ibn Sirin, from Abu Hurairah, from the Prophet, may Allah bless him and grant him peace, who said: "If a fly falls into the vessel of one of you, let him submerge it, for in one of its wings is a disease, and in the other is a cure." And 'Affan said once: "For one of its wings..."