The modern forgery claiming to be a letter of the Prpophet Muhammad, now inexplicably preserved in a museum as a genuine item. There, fixed it for you.

The letter Prophet Muhammad ﷺ sent to Heraclius of the Roman Empire is preserved at the museum in the King Hussain Mosque (Jordan).

There are several letters of the prophet to several heads of state, which have been recorded in literary sources. There are some documents out there, which are said to be the actual letters mentioned in these sources Scholars rightly take these to be forgeries. Here's why: