Jabir binAbdullah (RA) reported that a desert Arab swore allegiance to Allahs Messenger ﷺ . He suffered from a severe fever in Madinah (and) so he came to Allahs Messenger ﷺ saying: Muhammad, cancel my oath of allegiance, but Allahs Messenger ﷺ 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 Allahs Messenger ﷺ said: Madinah is like a furnace which drives away its impurity and purifies what is good.