Sayyiduna Usamah bin Zayd (may Allah be pleased with them both) narrates from the Messenger of Allah (peace and blessings be upon him) that he (peace and blessings be upon him) said: "This sickness - or illness - is a punishment with which some nations before you were punished; then it remained in the earth, sometimes going away and sometimes coming. So whoever hears of it in a land should not go there, and whoever is in a land where it breaks out, let fleeing not drive him out of it." (These are the words of al-Layth's narration.)
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 272