Musnad Ahmad 32:562

Hassan narrated to us, Hammad narrated to us, Sulaiman al-Taymi and Thabit informed us, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I came upon Musa on the night I was taken on the Night Journey (Isra) by the red sand dune, and he was standing, praying in his grave."