Hadith: If a fly falls into the drink of any one of you, he should dip it (in the drink) and then remove it, for in one of its wings there is a disease and in the other there is cure

عن أبي هريرة رضي الله عنه مرفوعاً: «إذا وقع الذباب في شراب أحدكم فليغمسه، ثم لينزعه؛ فإن في أحد جناحيه داء، وفي الآخر شفاء». وفي رواية: «وإنه يتقي بجناحه الذي فيه الداء».
[صحيح، وزيادة أبي داود صحيحة] - [رواه البخاري، والرواية الأخرى لأبي داود وأحمد]

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “If a fly falls into the drink of anyone of you, he should dip it (in the drink) and then remove it, for in one of its wings there is a disease and in the other there is cure.” Another narration adds: “It (the fly) protects itself with the wing that has the disease.”
Authentic hadith - Narrated by Bukhari

Explanation

The Prophet (may Allah's peace and blessings be upon him) informs us that if a fly falls into a drink, it does not affect it; rather, the person drinking should immerse the whole fly in the drink. The reason is that one of the fly’s wings carries a disease, and this is the wing that falls in the liquid. The other wing, however, carries the cure from that disease. Modern medicine has proven the validity of this piece of information, which Muslims have known for centuries; so, praise be to Allah for the blessing of Islam.