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

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ مُحَمَّدِ بْنِ الْمُنْكَدِرِ، عَنْ جَابِرِ، بْنِ عَبْدِ اللَّهِ أَنَّ أَعْرَابِيًّا، بَايَعَ رَسُولَ اللَّهِ ﷺ فَأَصَابَ الأَعْرَابِيَّ وَعَكٌ بِالْمَدِينَةِ فَأَتَى النَّبِيَّ ﷺ فَقَالَ يَا مُحَمَّدُ أَقِلْنِي بَيْعَتِي . فَأَبَى رَسُولُ اللَّهِ ﷺ ثُمَّ جَاءَهُ فَقَالَ أَقِلْنِي بَيْعَتِي . فَأَبَى ثُمَّ جَاءَهُ فَقَالَ أَقِلْنِي بَيْعَتِي . فَأَبَى فَخَرَجَ الأَعْرَابِيُّ فَقَالَ رَسُولُ اللَّهِ ﷺ " إِنَّمَا الْمَدِينَةُ كَالْكِيرِ تَنْفِي خَبَثَهَا وَيَنْصَعُ طَيِّبُهَا " .