(35) باب غَزْوَةِ الْحُدَيْبِيَةِ
The same narration was told by Majzaa from a man called Uhban bin Aus who was one of those who had witnessed (the Pledge of allegiance beneath) the Tree., and who had some trouble in his knee so that while doing prostrations, he used to put a pillow underneath his knee.
Reference: Sahih al-Bukhari 4174
In-book reference: Book 64, Hadith 216
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 59, Hadith 491