Yahya related to me from Malik from Zayd ibn Aslam that a manreceived a wound in the time of the Messenger of Allah, may Allahbless him and grant him peace. The blood clotted in the wound and theman called two men from the Banu Ammar tribe. They looked at it andclaimed that the Messenger of Allah, may Allah bless him and grant himpeace, said to them, "Which of you is the better doctor?" They said,"Is there any good in medicine, Messenger of Allah?" Zayd claimed thatthe Messenger of Allah, may Allah bless him and grant him peace, said,"The one who sent down the disease sent down the remedy."
USC-MSA web (English) reference: Book 50, Hadith 12
Arabic reference: Book 50, Hadith 1725