Abu Sa'id al-Khudri reported the Prophet as saying, "When a fly alights on food plunge it in, for one of its wings contains poison and the other a cure, and it puts the poison first and the cure second."
Ibn ‘Abbas said that the people of pre-Islamic times used to eat some things and leave others alone, considering them unclean. Then God sent His Prophet and sent down His Book, marking some things lawful and others unlawful; so what He made lawful is lawful, what He made unlawful is unlawful, and what He said nothing about is allowable. And he recited, ''Say, I do not find in what is revealed to me anything forbidden to him who eats it, except carrion or blood..." 1
1. Qur'an, vi, 145.
Abu Huraira reported God’s messenger as saying, "When a fly alights in the vessel of any of you plunge it in, for in one of its wings there is disease and in the other a cure; it puts forward the one containing the disease, so dip it all in."