It is narrated from Hazrat Ahmar bin Juz’ that when the Prophet (peace be upon him) would go into prostration, we would feel compassion for the Prophet (peace be upon him) at that time because he would exert great effort in separating his elbows from his sides.
Hadith Referenceمسند احمد / أول مسند البصريين / 20337
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن فى المتابعات والشواهد لأجل عباد بن راشد