Musnad Ahmad 33:501

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu al-Zubayr narrated to us, from Jabir, that the Messenger of Allah (peace and blessings of Allah be upon him) declared sacred what is between the two lava fields (harratayn) of Medina; no tree is to be cut from it, except for a man to feed his camel.