Musnad Ahmad 8:134

Ibn Numayr narrated to us, from Uthman—meaning Ibn Hakim—, Amir ibn Sa’d informed me, from his father, who said: The Messenger of Allah (ﷺ) said: "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 they only knew. No one leaves it, turning away from it, but that Allah replaces him with someone better than him. And no one remains steadfast through its hardships and its difficulties, but that I will be a witness for him or an intercessor on the Day of Resurrection."