Abu Huraira and Sa'd reported Allah's Messenger (way peace be upon him) as saying: O Allah, bless the people of Medina in their mudd, the rest of the hadith being the same, and in It (this is also mentioned):" He wo intends to do harm to its people, Allah would efface him just as salt it dissolved in water."
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، حَدَّثَنَا أُسَامَةُ بْنُ زَيْدٍ، عَنْ أَبِي عَبْدِ اللَّهِ الْقَرَّاظِ، قَالَ سَمِعْتُهُ يَقُولُ سَمِعْتُ أَبَا هُرَيْرَةَ، وَسَعْدًا، يَقُولاَنِ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " اللَّهُمَّ بَارِكْ لأَهْلِ الْمَدِينَةِ فِي مُدِّهِمْ " . وَسَاقَ الْحَدِيثَ وَفِيهِ " مَنْ أَرَادَ أَهْلَهَا بِسُوءٍ أَذَابَهُ اللَّهُ كَمَا يَذُوبُ الْمِلْحُ فِي الْمَاءِ " .
sunnah.com