Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) narrated that a Bedouin pledged allegiance to the Messenger of Allah (peace and blessings be upon him) for Islam. Then he was afflicted with fever in Madinah, so he came to the Messenger of Allah (peace and blessings be upon him) and said, "O Messenger of Allah, cancel my pledge." The Messenger of Allah (peace and blessings be upon him) refused. Then he came again and said, "Cancel my pledge." The Messenger of Allah (peace and blessings be upon him) refused again. Then he came and demanded the cancellation of his pledge. The Messenger of Allah (peace and blessings be upon him) refused again. After that, he left (Madinah) on his own. The Messenger of Allah (peace and blessings be upon him) said regarding this, "Madinah is like a furnace; it removes its impurities and retains the pure."