What is the ruling on keeping away from people who have a contagious disease?

Summary

There is a hadith commanding people to keep away from lepers, and scholars differ in understanding it. Some reject it because the Prophet once ate with a leper, while others authenticate it and cite Umar's practice and the Prophet's declining to shake hands at a pledge of allegiance. Ibn Battal held that the command to keep away does not contradict sitting with a leper, as it was not an obligatory command. In the Shafi'i school, those with contagious diseases are barred from mosques and public gatherings, and Ibn Hajar al-Haitami held this barring obligatory when harm is feared.

Written in our own words from the original fatwa — check the source before acting on it.