It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that a Bedouin pledged allegiance to the Messenger of Allah (peace and blessings be upon him) upon Islam, but he became feverish in Madinah. He came to the Messenger of Allah (peace and blessings be upon him) and said: O Messenger of Allah! Return my pledge to me. The Prophet (peace and blessings be upon him) refused. He came a second time and said: Return my pledge to me. The Prophet (peace and blessings be upon him) refused. He came a third time and said: Return my pledge to me. The Prophet (peace and blessings be upon him) refused. (Eventually, despite not being granted permission) the Bedouin left Madinah. The Messenger of Allah (peace and blessings be upon him) said: "Madinah is like a furnace and a bellows; it expels impure things and refines the pure."