Sahih Muslim
The Book Pertaining to the Excellent Qualities of the Holy Prophet (may Peace be upon them) and His Companions (Kitab Al-Fadail)
Book Number: 030 / Hadith Number: 5858
Anas b. malik reported Allah's Messenger (may peace be upon him) as saying: I came. And in the narration transmitted on the authority of Haddib (the words are): I happened to pass by Moses on the occasion of the Night journey near the red mound (and found him) saying his prayer in his grave.