Musnad Ahmad

Aamir bin Sa’d (may Allah have mercy on him) says that a man came to Hazrat Sa’d (may Allah be pleased with him) to ask about the plague. Hazrat Usama (may Allah be pleased with him) said, “I will tell you about it. I heard the Prophet Muhammad (peace and blessings be upon him) say: The plague is a punishment which Allah the Exalted sent upon the people before you (the Children of Israel). Sometimes it comes and sometimes it goes. Therefore, if an epidemic spreads in a region, do not go into that region, and if an epidemic spreads in a region where you are already present, do not flee from it.”