Musnad Ahmad 32:1038

Bahz narrated to us, Hammad narrated to us, Hisham ibn Zayd narrated to us, he said: I heard Anas ibn Malik say: The Messenger of Allah, peace and blessings of Allah be upon him, said: "If the Hour (the Day of Resurrection) is established while in the hand of one of you is a sapling, then if he is able not to stand up until he plants it, let him do so."