Ahmar,the Companion of the Messenger of Allah (ﷺ), narrated to us:
"Weused to feel sorry for the Messenger of Allah (ﷺ) because hetookpains to keep his arms away from his sides when he prostrated." (IT)
English reference (IT): Vol. 1, Book 5, Hadith 886 (IT)
Arabic reference (IT): Book 5, Hadith 936 (IT)