Musnad Ahmad 30:2120

Musa ibn Dawud narrated to us, he said: Ibn Lahi'ah narrated to us, from Abu Yunus, from Abu Hurairah, from the Messenger of Allah, peace and blessings of Allah be upon him, who said: "Indeed, in Paradise there is a tree; a rider on a swift horse travels in its shade for one hundred years, and its leaves cover Paradise."