Sahih Muslim
Sahih Muslim 1382 a
Al-Madinah eliminates its Dross and it is also called Tabah, and Taibah
Arabic hadith text
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكِ بْنِ أَنَسٍ، - فِيمَا قُرِئَ عَلَيْهِ - عَنْ يَحْيَى بْنِ، سَعِيدٍ قَالَ سَمِعْتُ أَبَا الْحُبَابِ، سَعِيدَ بْنَ يَسَارٍ يَقُولُ سَمِعْتُ أَبَا هُرَيْرَةَ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم "أُمِرْتُ بِقَرْيَةٍ تَأْكُلُ الْقُرَى يَقُولُونَ يَثْرِبَ وَهْىَ الْمَدِينَةُ تَنْفِي النَّاسَ كَمَا يَنْفِي الْكِيرُ خَبَثَ الْحَدِيدِ " .
Translation
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (way peace be upon him) as saying
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.