Sahih Muslim Book 7, Hadith Number 3168.

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.

Abu Huraira (Allah be pleased with him) reported: If I were to see deer grazing in Medina, I would have never molested them, for Allah’s Messenger (may peace be upon him) has stated: There is between the two lava mountains a sacred territory.