Ash-Shama'il Al-Muhammadiyah, Book 10, Hadith 71 (English)

Qataadah radiallahu anhu reports that: "I asked Anas to describe the shoe of Rasulullah Sayyidina Rasulullah sallallahu alaihe wasallam". He replied: "Each shoe had two straps"

حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، قَالَ‏:‏ حَدَّثَنَا أَبُو دَاوُدَ الطَّيَالِسِيُّ، قَالَ‏:‏ حَدَّثَنَا هَمَّامٌ، عَنْ، قَالَ‏:‏ قُلْتُ لأَنَسِ بْنِ مَالِكٍ‏:‏ كَيْفَ كَانَ نَعْلُ رَسُولِ اللهِ صلى الله عليه وسلم‏؟‏ قَالَ‏:‏ لَهُمَا قِبَالانِ‏.‏

also referenced under: Book 11, Hadith 75 (In-Book)