Narrated Ahmar ibn Jaz: When the Messenger of Allah ﷺ prostrated himself, he kept his arms far away from his sides so much so that we took pity on him.
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
900. Commentary:
That is, he (sallallahu alayhi wa sallam) would keep his arms well away from his sides, to such an extent that those who saw him would feel compassion, thinking that he was enduring great hardship. However, this posture is not possible in congregation or in the prayer row. Nevertheless, if due to old age or illness someone is unable to do so, then there is concession for him to perform prostration (sujud) in whatever manner he is able.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 900