Allah named Medina as Tabba. (Using translation from Muslim 1385)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ «إِنَّ اللهَ سَمَّى الْمَدِينَةَ طَابَةَ»  

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. (Using translation from Muslim 1382a)  

قَالَ رَسُولُ اللهِ ﷺ أُمِرْتُ بِقَرْيَةٍ تَأْكُلُ الْقُرَى يَقُولُونَ يَثْرِبُ وَهِيَ الْمَدِينَةُ تَنْفِي النَّاسَ كَمَا يَنْفِي الْكِيرُ خَبَثَ الْحَدِيدِ  

A bedouin came to the Prophet ﷺ and gave a pledge of allegiance for embracing Islam. The next day he came with fever and said (to the Prophet ﷺ ), "Please cancel my pledge (of embracing Islam and of emigrating to Medina)." The Prophet ﷺ refused (that request) three times and said, "Medina is like a furnace, it expels out the impurities (bad persons) and selects the good ones and makes them perfect." (Using translation from Bukhārī 1883)   

جَاءَ رَجُلٌ إِلَى النَّبِيِّ ﷺ فَبَايَعَهُ عَلَى الْإِسْلَامِ فَجَاءَ مِنَ الْغَدِ مَحْمُومًا فَقَالَ أَقِلْنِي ثَلَاثَ مَرَّاتٍ فَقَالَ رَسُولُ اللهِ ﷺ «الْمَدِينَةُ كَالْكِيرِ تَنْفِي خَبَثَهَا وَيَنْصَعُ طِيبُهَا»