Sayyiduna Anas (may Allah be pleased with him) reports that the Prophet (peace and blessings be upon him) said: "There is no significance to the contagion (of disease) or to the hamah; who infected the first one?"
(Allamah al-Haythami says:) I say: In the "Sahih" this part of it is recorded: "There is no significance to contagion."
Imam al-Bazzar recorded it, and its narrators are the narrators of the Sahih, except Ali bin al-Husayn al-Dirhami, and he is thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطب / 8393