(88) باب الْمَدِينَةِ تَنْفِي شِرَارَهَا
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.
Reference: Sahih Muslim 1382 a
In-book reference: Book 15, Hadith 557
USC-MSA web (English) reference(deprecated numbering scheme): Book 7, Hadith 3189