Sahih Muslim Book 7, Hadith Number 3160.

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.

‘Asim reported: I asked Anas (Allah be pleased with him) whether Allah’s Messenger (may peace be upon him) had declared Medina as sacred. He said: Yes, it is sacred, so its tree is not to be cut; and he who did that let the curse of Allah and that of the angels and of all people be upon him.