It was narrated from Maimunah that when the Prophet ﷺ prostrated, he would hold his forearms away from his sides, such that if a lamb wanted to pass under his arms, it would be able to do so.
أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا سَجَدَ جَافَى يَدَيْهِ فَلَوْ أَنَّ بَهْمَةً أَرَادَتْ أَنْ تَمُرَّ بَيْنَ يَدَيْهِ لَمَرَّتْ