Whenever the Prophet ﷺ used to offer prayer he used to keep arms away (from the body) so that the whiteness of his armpits was visible.  

أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ وَقَالَ اللَّيْثُ حَدَّثَنِي جَعْفَرُ بْنُ رَبِيعَةَ نَحْوَهُ  

Ibn Buhaina, "When the Prophet ﷺ prayed, he used to separate his arms from his body so widely that the whiteness of his armpits was visible."  

أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ وَقَالَ اللَّيْثُ حَدَّثَنِي جَعْفَرُ بْنُ رَبِيعَةَ نَحْوَهُ  

When the Prophet ﷺ prostrated, lie spread out his arms so that the whiteness of his armpits was visible.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ  

When the Messenger of Allah ﷺ prayed he held his arms out so much that the whiteness of his armpits appeared. (Using translation from Nasāʾī 1106)  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ  

[Machine] "The Prophet ﷺ used to raise his hands and spread them in front of him during prostration until the whiteness of his armpits was visible."  

«كَانَ النَّبِيُّ ﷺ إِذَا سَجَدَ فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُوَ بَيَاضُ إِبْطَيْهِ»  

When the Prophet ﷺ prostrated, lie spread out his arms so that the whiteness of his armpits was visible. (Using translation from Muslim 495a)  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يَبْدُو بَيَاضَ إِبِطَيْهِ  

[Machine] Indeed, the Messenger of Allah, may ﷺ , used to raise his arms until his armpits could be seen when he prayed.  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا صَلَّى فَرَّجَ بَيْنَ يَدَيْهِ حَتَّى يُرَى بَيَاضُ إِبِطَيْهِ