Malik related to me that Yahya ibn Said said, "I heardAbu'l-Hubab Said ibn Yasar say that he heard Abu Hurayra say that heheard the Messenger of Allah, may Allah bless him and grant him peace,say, 'I was ordered to a town which will eat up towns. They used tosay, 'Yathrib,' but it is Madina. It removes the bad people like theblacksmith's furnace removes impurities from the iron.' " (FR)
USC-MSA web (English) reference: Book 45, Hadith 5 (FR)
Arabic reference (FR): Book 45, Hadith 1605 (FR)