The sandals of the Messenger of Allah ﷺ had two straps each.
حدثنا يزيد أخبرنا همام بن يحيى عن قتادة
كانت نعال رسول الله ﷺ لهما قبالان
No references are available.
Its isnad is sahih. The hadith is found in Bukhari 10/312 no. 5857 (Fath), Abu Dawud 4/69 no. 4134, and Tirmidhi 4/242 no. 1773, where he said, hasan sahih, all of them in the Book of Clothing, and Nasai in "Adornment" 8/217 no. 5367, and Ibn Majah 2/1194 no. 3615, in the Book of Clothing.