Musnad Ahmed: Hadith 4170

The Messenger of Allah (ﷺ) stood up among us and said: “Nothing infects anything else, nothing infects anything else.” A Bedouin stood up and said: O Messenger of Allah, (how come) the first sign of scabies could appear on the lips of the camel or its tail among a large number of camels and infect all of them? The Messenger of Allah (ﷺ) said: "So what caused the first one to be infected? There is no 'adwa (contagion, transmission of infectious disease without the permission of Allah), no hamah (refers to a Jahili Arab tradition described variously as: a worm which infests the grave of a murder victim until he is avenged; an owl; or the bones of a dead person turned into a bird that could fly), and no Safar (the month of Safar was regarded as "unlucky” during the Jahiliyyah). Allah created each soul and decreed its life, its calamities and its provision."