He saw the Messenger of Allah ﷺ lying on his back in the mosque with one leg placed over the other.
قال حدثنا حجاج بن محمد عن ابن جريج قال أخبرني يحيى بن جرجة عن ابن شهاب
أنه أبصر رسول الله ﷺ مستلقيا في المسجد على ظهره واضعا إحدى رجليه على الأخرى
Its isnad is sahih. Yahya bin Jarjah has been mentioned before, though not much, and he is trustworthy. Ibn Hibban rated him trustworthy (7/599), and Abu Hatim said, "A shaykh," in Al-Jarh (9/133), while Bukhari made no comment on him in Al-Kabir (8/266). The hadith has already appeared at 16390.