Musnad Ahmad 32:1120

Yazid ibn Harun narrated to us, Asim informed us, he said: I asked Anas ibn Malik, "Did the Messenger of Allah, peace and blessings of Allah be upon him, make Medina a sanctuary?" He said: "Yes, it is a sanctuary. Allah and His Messenger have made it a sanctuary. Its vegetation must not be cut. Whoever does that, upon him is the curse of Allah, the angels, and all of mankind."