A bedouin came to the Prophet (ﷺ) and gave a pledge of allegiance for embracing Islam. The next day hecame with fever and said (to the Prophet (ﷺ) ), "Please cancel my pledge (of embracing Islam and ofemigrating to Medina)." The Prophet (ﷺ) refused (that request) three times and said, "Medina is like afurnace, it expels out the impurities (bad persons) and selects the good ones and makes them perfect."