"Al-Bara' described the prostration to us. He places his hands on the ground and raised his posterior and said: 'This is what I saw the Messenger of Allah ﷺ doing."  

وَصَفَ لَنَا الْبَرَاءُ السُّجُودَ فَوَضَعَ يَدَيْهِ بِالأَرْضِ وَرَفَعَ عَجِيزَتَهُ وَقَالَ هَكَذَا رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَفْعَلُ  

When the Messenger of Allah ﷺ prayed he would Jakhkha.  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا صَلَّى جَخَّى  

When the Messenger of Allah ﷺ prayed he held his arms out so much that the whiteness of his armpits appeared.  

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

"If I were in front of the Messenger of Allah ﷺ I would be able to see the whiteness of his armpits." (One of the narrators) Abu Mijlaz said: "It is as if he said that because he was praying."  

لَوْ كُنْتُ بَيْنَ يَدَىْ رَسُولِ اللَّهِ ﷺ لأَبْصَرْتُ إِبْطَيْهِ قَالَ أَبُو مِجْلَزٍ كَأَنَّهُ قَالَ ذَلِكَ لأَنَّهُ فِي صَلاَةٍ  

"I prayed with the Messenger of Allah ﷺ and I used to see the whiteness of his armpits when he prostrated."  

صَلَّيْتُ مَعَ رَسُولِ اللَّهِ ﷺ فَكُنْتُ أَرَى عُفْرَةَ إِبْطَيْهِ إِذَا سَجَدَ