A bedouin gave the Pledge of allegiance for embracing Islam to Messenger of Allah ﷺ, and then he got an attack of fever in Medina and came to Messenger of Allah ﷺ: and said, "O Messenger of Allah ﷺ! Cancel my pledge." Messenger of Allah ﷺ refused to do so. The bedouin came to him again and said, "Cancel my pledge," but he refused again, and then again, the bedouin came to him and said, "Cancel my pledge," and Messenger of Allah ﷺ refused. The bedouin finally went away, and Messenger of Allah ﷺ said, "Medina is like a pair of bellows (furnace), it expels its impurities while it brightens and clears its good.'
أَنَّ أَعْرَابِيًّا بَايَعَ رَسُولَ اللَّهِ ﷺ عَلَى الإِسْلاَمِ فَأَصَابَ الأَعْرَابِيَّ وَعْكٌ بِالْمَدِينَةِ فَجَاءَ الأَعْرَابِيُّ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ 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 طِيبُهَا