Sunan an-Nasa'i, Volume 6, Book 48, Hadith 5370 (DarusSalam) ⓘ
It was narrated that 'Amr bin Aws said: "The sandals of the Messenger of Allah [SAW] had two straps."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا صَفْوَانُ بْنُ عِيسَى، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ مُحَمَّدٍ، عَنْ عَمْرِو بْنِ أَوْسٍ، قَالَ كَانَ لِنَعْلِ رَسُولِ اللَّهِ صلى الله عليه وسلم قِبَالاَنِ .
also referenced under: Hadith 5368 (Reference) & Book 48, Hadith 329 (In-Book)