Musnad Ahmad 32:1859

Ali ibn Ishaq narrated to us, Abdullah narrated to us, he said: Ubaydullah ibn Mawhab informed us, from Malik ibn Muhammad ibn Harithah al-Ansari: That Anas ibn Malik said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no man who raises his tongue with a truth that is acted upon after him, except that its reward is made to flow for him until the Day of Resurrection. Then Allah will fulfill his reward for him on the Day of Resurrection."