It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The concept of contagious disease is not correct, there is no reality to bad omens, there is no truth to the month of Safar or the owl being inauspicious." A man said: O Messenger of Allah! Among a hundred camels, if a mangy camel joins them, it makes all of them mangy (and you say that disease is not contagious?). The Prophet (peace and blessings be upon him) said: "Tell me! Who afflicted the first camel with mange?"
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 3031
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، سماك بن حرب عن عكرمة مضطرب، قد توبع