God promised to save the dead body Firaun as a sign to the people! 

Verse 92 of Chapter 10:

"This day We shall salvage your body so that you may be a sign for those after you; and indeed most people are neglectful of Our signs."

God's words have now been proven fully based on both the discovery of Firaun's preserved dead body and the reality that most of the people are ignorant of His signs include this.