Hadith 184

Bulugh al-Maram

Book 2: The Book of Prayer
Hadith 184
وَعَنْ اِبْنِ بُحَيْنَةَ ‏- رضى الله عنه ‏- { أَنَّ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ , حَتَّى يَبْدُوَ بَيَاضُ إِبِطَيْهِ } مُتَّفَقٌ عَلَيْهِ .‏ 1‏
Ibn Buhainah (RA):

When the Prophet (ﷺ) prostrated while praying, he used to spread out his arms so that the whiteness of his armpits would be visible. [Agreed upon].