Musannaf Ibn Abi Shayba 36:41

Al-Hasan ibn Musa narrated to us, he said: Hammad ibn Salamah narrated to us, he said: Sulayman al-Taymi and Thabit al-Bunani informed us, from Anas, 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), at the red sand dune, and he was standing, praying in his grave."