The Prophet's ﷺ sandal had two straps.
حدثنا مسلم بن إبراهيم حدثنا همام عن قتادة
أن نعل النبي ﷺ كان لها قبالان
No references are available.
Bukhari narrated it in the Book of Clothing, Chapter "Two straps on a sandal, and whoever considers one wide strap sufficient," hadith no. 5857, from the hadith of Hammam, through this same chain.