Sahih Muslim Book 7, Hadith Number 3177.

Chapter : Eminence of Medina, Allah’s Apostle (may peace be upon him) showered blessings upon it. Its sacredness and unlawfulness of hunting and lopping of trees and demarcation its precincts.

Sahl b. Hunif reported that Allah’s Messenger (may peace be upon him) pointed with his hands towards Medina and said: That is a sacred territory and a place of safety.