Chapter 29: Virtues of Madinah
Narrated Zaid bin Thabit: When the Prophet (ﷺ) went out for (the battle of) Uhud, some of his companions (hypocrites) returned
(home). A party of the believers remarked that they would kill those (hypocrites) who had returned,
but another party said that they would not kill them. So, this Divine Inspiration was revealed: "Then
what is the matter with you that you are divided into two parties concerning the hypocrites." ( 4.88)
The Prophet (ﷺ) said, "Medina expels the bad persons from it, as fire expels the impurities of iron."
Sahih al-Bukhari 1884