Musannaf Ibn Abi Shayba 35:172

Ibn Numayr narrated to us, from Uthman ibn Hakim, from Amir ibn Sa'd, from his father, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, I declare sacred what is between the two lava fields of Medina, that its thorny trees should not be cut, nor its game be killed." And he said: "Medina is better for them, if only they knew."