Jabir b. 'Abdullah (Allah be pleased with them) reported that a desert Arab swore allegiance to Allah' s Messenger (ﷺ). He suffered from a severe fever in Medina (and) so he came to Allah' s Messenger (ﷺ) saying: Muhammad, cancel my oath of allegiance. But Allah' s 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 Allah' s Messenger (ﷺ) said: Medina is like a furnace which drives away its impurity and purifies what is good.