Musnad Ahmad 30:2704

Hajjaj narrated to us, he said: Layth ibn Sa'd narrated to us, he said: Sa'id ibn Abi Sa'id al-Maqburi narrated to me, from his father, from Abu Hurayrah, from the Messenger of Allah, may Allah bless him and grant him peace, who said: "Indeed, in Paradise there is a tree in whose shade a rider travels for one hundred years."