Musnad Ahmad 792:10

Hassan narrated to us, saying: Hammad narrated to us, from what I heard him say, he said: And I heard al-Jurayri narrating, from Hakim ibn Mu'awiyah, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "You complete seventy nations; you are the last of them, and the most noble of them to Allah. And between the two leaves of the gates of Paradise is a journey of forty years, and there shall surely come upon it a day when it is crowded."