Musnad Ahmad 28:380

Ali ibn Ishaq narrated to us, Abdullah informed us, Sa'id ibn Yazid informed us, from Abu al-Samh, from Isa ibn Hilal al-Sadafi, from Abdullah ibn Amr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If a lead ball like this—and he pointed to something like a skull—were sent from the sky to the earth, and it is a journey of five hundred years, it would reach the earth before nightfall. And if it were sent from the top of the chain, it would travel for forty autumns, night and day, before it reached its base or its bottom."