Musnad Ahmad 33:565

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu al-Zubayr narrated to us, Jabir ibn Abdullah informed me, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "A time will surely come upon Medina when people will depart from it to the horizons, seeking prosperity, and they will find prosperity. Then they will come and transport their families to the prosperity, while Medina is better for them, if only they knew."