Volume 3, Book 30, Number 107:
Narrated Jabir:
A bedouin came to the Prophet and gave a pledge of allegiance for embracing Islam. The next day
he came with fever and said (to the Prophet ), “Please cancel my pledge (of embracing Islam and of
emigrating to Medina).” The Prophet refused (that request) three times and said, “Medina is like a
furnace, it expels out the impurities (bad persons) and selects the good ones and makes them per –
fect.”