Sunan Ibn Majah, Book 5, Hadith 936 (In-Book) ⓘ
Ahmar, the Companion of the Messenger of Allah, narrated to us: “We used to feel sorry for the Messenger of Allah because he took pains to keep his arms away from his sides when he prostrated.”
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا عَبَّادُ بْنُ رَاشِدٍ، عَنِ الْحَسَنِ، حَدَّثَنَا أَحْمَرُ، صَاحِبُ رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ قَالَ إِنْ كُنَّا لَنَأْوِي لِرَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ مِمَّا يُجَافِي بِيَدَيْهِ عَنْ جَنْبَيْهِ إِذَا سَجَدَ .
also referenced under: Hadith 886 (Reference) & Volume 2, Book 5, Hadith 886 (DarusSalam)