Musnad Ahmad 8:167

'Affan narrated to us, 'Abd al-Wahid ibn Ziyad narrated to us, 'Uthman ibn Hakim informed us, 'Amir ibn Sa'd narrated to me, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, I declare sacred what is between the two lava fields of Medina, just as Abraham declared Mecca sacred. Its thorny trees are not to be cut, its game is not to be hunted, and no one leaves it, desiring something else, but that Allah replaces him with someone better than him. And Medina is better for them, if they only knew. No one intends evil for its people but that Allah will melt him as lead is melted in the fire, or as salt is melted in water."