Musnad Abu Ya'la al-Mawsili 135:5

Abu Bakr narrated to us, Yazid bin Harun narrated to us, from Asim, who said: I asked Anas bin 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."