Sahih Muslim Book 7, Hadith Number 3199.

Chapter : Allah will punish those who intend to do any harm to the citizens of Medina.

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 who intends to do harm to its people, Allah would efface him just as salt it dissolved in water.”