A time will come for the people (of Medina) when a man will invite his cousin and any other near relation: Come (and settle) at (a place) where living is cheap, come to where there is plenty, but Medina will be better for them; would they know it! By Him in Whose Hand is my life, none amongst them would go out (of the city) with a dislike for it, but Allah would make his successor in it someone better than be. Behold. Medina is like furnace which eliminates from it the impurities. And the Last Hour will not come until Medina banishes its evils just as a furnace eliminates the impurities of iron.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ يَأْتِي عَلَى النَّاسِ زَمَانٌ يَدْعُو الرَّجُلُ ابْنَ عَمِّهِ وَقَرِيبَهُ هَلُمَّ إِلَى الرَّخَاءِ هَلُمَّ إِلَى الرَّخَاءِ وَالْمَدِينَةُ خَيْرٌ لَهُمْ لَوْ كَانُوا يَعْلَمُونَ وَالَّذِي نَفْسِي بِيَدِهِ لاَ يَخْرُجُ مِنْهُمْ أَحَدٌ رَغْبَةً عَنْهَا إِلاَّ أَخْلَفَ اللَّهُ فِيهَا خَيْرًا مِنْهُ أَلاَ إِنَّ الْمَدِينَةَ كَالْكِيرِ تُخْرِجُ الْخَبِيثَ لاَ تَقُومُ السَّاعَةُ حَتَّى تَنْفِيَ الْمَدِينَةُ شِرَارَهَا كَمَا يَنْفِي الْكِيرُ خَبَثَ الْحَدِيدِ  

I have been commanded (to migrate) to a town (Medina) which would overpower other towns. They (the people) call it Yathrib; its correct name is (in fact) Medina. It eliminates (bad) people just as a furnace removes the alloy of iron.  

قَالَ رَسُولُ اللَّهِ ﷺ أُمِرْتُ بِقَرْيَةٍ تَأْكُلُ الْقُرَى يَقُولُونَ يَثْرِبَ وَهْىَ الْمَدِينَةُ تَنْفِي النَّاسَ كَمَا يَنْفِي الْكِيرُ خَبَثَ الْحَدِيدِ  

" Just as a furance removes impurity," but no mention is made of iron.  

عَنْ يَحْيَى بْنِ سَعِيدٍ بِهَذَا الإِسْنَادِ وَقَالاَ كَمَا يَنْفِي الْكِيرُ الْخَبَثَ لَمْ يَذْكُرَا الْحَدِيدَ  

Muhammad, cancel my oath of allegiance. But Messenger of Allah 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 Messenger of Allah ﷺ said: Medina is like a furnace which drives away its impurity and purifies what is good.  

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  

It is Taiba, thereby meaning Medina. It drives away impurity just as fire removes the impurity of silver.  

عَنِ النَّبِيِّ ﷺ قَالَ إِنَّهَا طَيْبَةُ يَعْنِي الْمَدِينَةَ وَإِنَّهَا تَنْفِي الْخَبَثَ كَمَا تَنْفِي النَّارُ خَبَثَ الْفِضَّةِ  

Allah named Medina as Tabba.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ إِنَّ اللَّهَ تَعَالَى سَمَّى الْمَدِينَةَ طَابَةَ