When the Messenger of Allah ﷺ prostrated, he kept his hands so much apart from each other that when it was seen from behind the armpits became visible. Waki' said: That is their whiteness.  

كَانَ رَسُولُ اللَّهِ ﷺ إِذَا سَجَدَ جَافَى حَتَّى يَرَى مَنْ خَلْفَهُ وَضَحَ إِبْطَيْهِ قَالَ وَكِيعٌ يَعْنِي بَيَاضَهُمَا  

[Machine] The Prophet Muhammad ﷺ used to lean forward while performing prostration until the whiteness of his armpits was visible to those behind him.  

كَانَ النَّبِيُّ ﷺ إِذَا سَجَدَ جَافَى حَتَّى يَرَى مَنْ خَلْفَهُ بَيَاضَ إِبْطَيْهِ  

[Machine] The Messenger of Allah ﷺ used to lower himself down in prostration until the whiteness of his armpits could be seen by those behind him.  

كَانَ رَسُولُ اللهِ ﷺ إِذَا سَجَدَ جَافَى حَتَّى يَرَى مَنْ خَلْفَهُ بَيَاضَ إِبْطَيْهِ  

[Machine] The Prophet ﷺ used to straighten up in sujood (prostration) until he could see the one behind him and his armpits became visible.  

كَانَ النَّبِيُّ ﷺ «إِذَا سَجَدَ جَافَى حَتَّى يَرَى مَنْ خَلْفَهُ وَضَحَ إِبِطَيْهِ»  

When the Messenger of Allah ﷺ prostrated himself, he spread his arms, i. e. he separated them so much that the whiteness of his armpits became visible from behind and when he sat (for Jalsa) he rested on his left thigh. (Using translation from Muslim 497a)  

عَنْ مَيْمُونَةَ زَوْجِ النَّبِيِّ ﷺ قَالَتْ كَانَ رَسُولُ اللَّهِ ﷺ إِذَا سَجَدَ خَوَّى بِيَدَيْهِ يَعْنِي جَنَّحَ حَتَّى يُرَى وَضَحُ إِبْطَيْهِ مِنْ وَرَائِهِ وَإِذَا قَعَدَ اطْمَأَنَّ عَلَى فَخِذِهِ الْيُسْرَى  

[Machine] Narrated Maymuna bint Al-Harith, the wife of the Prophet Muhammad ﷺ , said, "When the Messenger of Allah ﷺ prostrated, his back would become hollowed and his armpits would widen open."  

عَنْ مَيْمُونَةَ بِنْتِ الْحَارِثِ زَوْجِ النَّبِيِّ ﷺ قَالَتْ كَانَ رَسُولُ اللهِ ﷺ «إِذَا سَجَدَ جَافَى حَتَّى يُرَى خَلْفُهُ وَفَتَحَ إِبْطَيْهِ»