Musnad Ahmad 30:502

'Abd al-Razzaq and 'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no contagion, no Safar, and no Hamah." A Bedouin said: "What about the camels that are in the sand as if they were gazelles, then a mangy camel mixes with them and makes them mangy?" The Prophet (peace and blessings of Allah be upon him) said: "Then who infected the first one?"