كتاب الحج
15  
The Book of Pilgrimage
(89)
Chapter: The prohibition of wishing ill towards the people of Al-Madinah, and that the one who wishes them ill will be caused to melt by Allah
(89)
باب مَنْ أَرَادَ أَهْلَ الْمَدِينَةِ بِسُوءٍ أَذَابَهُ اللَّهُ ‏‏
Sahih Muslim 1387 a

Sa'd b. Abu Waqqas reported Allah's Messenger (ﷺ) as saying:

He who intends to do harm to the people of Medina, Allah would efface him just as water dissolves salt.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا حَاتِمٌ، - يَعْنِي ابْنَ إِسْمَاعِيلَ - عَنْ عُمَرَ بْنِ نُبَيْهٍ، أَخْبَرَنِي دِينَارٌ الْقَرَّاظُ، قَالَ سَمِعْتُ سَعْدَ بْنَ أَبِي وَقَّاصٍ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ مَنْ أَرَادَ أَهْلَ الْمَدِينَةِ بِسُوءٍ أَذَابَهُ اللَّهُ كَمَا يَذُوبُ الْمِلْحُ فِي الْمَاءِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1387a
In-book reference : Book 15, Hadith 565
USC-MSA web (English) reference : Book 7, Hadith 3197
  (deprecated numbering scheme)