Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 615
Narrated Abu Huraira:
Allah's Apostle said, 'There is no 'Adha (no disease is conveyed from the sick to the healthy without Allah's permission), nor Safar, nor Hama." A bedouin stood up and said, "Then what about my camels? They are like deer on the sand, but when a mangy camel comes and mixes with them, they all get infected with mangy." The Prophet said, "Then who conveyed the (mange) disease to the first one?"