It's apparently from a muslim religious text. I found this very interesting because it's a rule that covers both self-preservation ("don't enter the infected zone") and quarantine ("if infected, stay where you are"). It's an early containment protocol.

What seems most fascinating to me is that by proscribing this from a religious channel, you can circumvent psychological mechanisms that would otherwise cause people to act in their own self interest - and in this case it actually works for the greater good.