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. (Using translation from Muslim 2375a)
"أَتَيْتَ على موسى ليلةَ أُسْرِى بي عند الكثيبِ الأحمرِ، وهو قائمٌ يصلى في قبرهِ".