Muwatta Imam Malik (Riwayat Ibn al-Qasim)

It is narrated from Sayyiduna Jabir bin Abdullah (al-Ansari, may Allah be pleased with him) that a Bedouin pledged allegiance to the Messenger of Allah, peace and blessings be upon him, for Islam (and to remain in Madinah). Then that Bedouin became feverish in Madinah, so he came to the Prophet, peace and blessings be upon him, and said: "O Messenger of Allah! Cancel my pledge." The Prophet, peace and blessings be upon him, refused, so he came again and said: "Cancel my pledge." The Prophet, peace and blessings be upon him, refused, so he came a third time and said: "Cancel my pledge." The Prophet, peace and blessings be upon him, refused, then that Bedouin left (Madinah) and went away. The Prophet, peace and blessings be upon him, then said: "Madinah is like a furnace of a goldsmith; it removes impurities and filth and refines and brightens the good."

It is narrated from Sayyiduna Sufyan bin Zuhair (may Allah be pleased with him) that I heard the Messenger of Allah (peace and blessings be upon him) say: Yemen will be conquered, then a people will come (and leave Madinah), they will take their families and dependents with them, even though Madinah would be better for them if they knew. Iraq will be conquered, then a people will come who will travel taking their families and dependents with them, even though Madinah would be better for them if they knew. And Shaam will be conquered, then a people will come who will travel taking their families and dependents with them, and Madinah would be better for them if they knew. And Shaam will be conquered, then a people will come who will travel taking their families and dependents with them, and Madinah would be better for them if they knew.

It is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: "I have been commanded regarding a town which consumes (i.e., prevails over) other towns. People call it Yathrib, and it is Madinah. It expels evil people just as a furnace expels the impurities of iron."