Authentic
Sunan Ibn Majah 886
“We used to feel sorry for the Messenger of Allah (ﷺ) because he took pains to keep his arms away from his sides when he prostrated.”
إِنْ كُنَّا لَنَأْوِي لِرَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ مِمَّا يُجَافِي بِيَدَيْهِ عَنْ جَنْبَيْهِ إِذَا سَجَدَ .