Sahih Bukhari Volume 7, Book 71, Hadith Number 665A.

Narrated By Abu Huraira : The Prophet said, ‘No ‘Adha (i.e. no contagious disease is conveyed to others without Allah’s permission); nor (any evil omen m the month of) Safar; nor Hama” A Bedouin said, “O Allah’s Apostle! What about the camels which, when on the sand (desert) look like deers, but when a mangy camel mixes with them they all get infected with mange?” On that Allah s Apostle said, “Then who conveyed the (mange) disease to the first (mangy) camel?”