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."
حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ عَدِيِّ بْنِ ثَابِتٍ، سَمِعْتُ عَبْدَ اللَّهِ بْنَ يَزِيدَ،، يُحَدِّثُ عَنْ زَيْدِ بْنِ ثَابِتٍ ـ رضى الله عنه ـ قَالَ لَمَّا خَرَجَ النَّبِيُّ صلى الله عليه وسلم إِلَى أُحُدٍ، رَجَعَ نَاسٌ مِمَّنْ خَرَجَ مَعَهُ، وَكَانَ أَصْحَابُ النَّبِيِّ صلى الله عليه وسلم فِرْقَتَيْنِ، فِرْقَةً تَقُولُ نُقَاتِلُهُمْ‏.‏ وَفِرْقَةً تَقُولُ لاَ نُقَاتِلُهُمْ‏.‏ فَنَزَلَتْ ‏{‏فَمَا لَكُمْ فِي الْمُنَافِقِينَ فِئَتَيْنِ وَاللَّهُ أَرْكَسَهُمْ بِمَا كَسَبُوا‏}‏ وَقَالَ ‏"‏ إِنَّهَا طَيْبَةُ تَنْفِي الذُّنُوبَ كَمَا تَنْفِي النَّارُ خَبَثَ الْفِضَّةِ ‏"‏‏.‏