Sahih al-Bukhari 4050

Narrated Zaid bin Thabit:When the Prophet (ﷺ) set out for (the battle of) Uhud, some of those who had gone out with him, returned. The companions of the Prophet (ﷺ) were divided into two groups. One group said, "We will fight them (i.e. the enemy)," and the other group said, "We will not fight them." So there came the Divine Revelation:-- '(O Muslims!) Then what is the matter within you that you are divided. Into two parties about the hypocrites? Allah has cast them back (to disbelief) Because of what they have earned.' (4.88) On that, the Prophet (ﷺ) said, "That is Taiba (i.e. the city of Medina) which clears one from one's sins as the fire expels the impurities of silver."