Musnad Abu Ya'la al-Mawsili 117:51

Hadaba and Shayban narrated to us, they said: Hammad bin Salamah narrated to us, from Thabit, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "I passed by Musa on the night I was taken on the Night Journey, and he was standing, praying in his grave at the red sand dune."