Jabir bin'Abdullah (RA) reported that a desert Arab swore allegiance to Allah's Messenger ( صلی اللہ علیہ وسلم ) . He suffered from a severe fever in Madinah (and) so he came to Allah's Messenger ( صلی اللہ علیہ وسلم ) saying: Muhammad, cancel my oath of allegiance, but Allah's Messenger ( صلی اللہ علیہ وسلم ) refused it. He again came and said: Cancel my oath of allegiance, but he (the Holy Prophet) refused it. He again came to him and said: Cancel my oath of allegiance, but he refused. The desert Arab, however, went away (cancelling the allegiance himself); thereupon Allah's Messenger ( صلی اللہ علیہ وسلم ) said: Madinah is like a furnace which drives away its impurity and purifies what is good.